17 June, 2020:

• The page on Rare Numbers updated (including list up to 10²³).

• Prime curios 11, 1427, 44936, 120689, 132882, 480585, 206913578, 511733945 and many more added.

14 December, 2019:

• The page on Rare Numbers updated (including list up to 10²²).

• CYF NO. 49 Comments by Daniel Suteu given.

• CYF NO. 51 Comments by Jens Kruse Andersen given.

• Prime curios 12, 182, 10342, 49141, 10234567 and many more added.

15 September, 2019:

• The page on Fascinating Triangular Numbers updated and enlarged.

• The page on Rare Numbers updated.

• CYF NO. 50 Solution by Al Zimmermann, Brian Trial, Emmanuel Vantieghem and Alessandro Casini given.

• Prime curios 11,13,19,31,107,127,199,373,712,797,919,929,1213,1217,1229,1279,1586,3169,3257,4514,5701,7613,7739,11047,15841,16561,21023,35731,38069,46099,100049,
  105683,176861,494639,670033,1015423,1059443,1148527,1324913,1460189,1530787,2012101,5133127,10152463,57486888,941056273,987654301,1012356487,1041293663,
  1123456798,1123548967,1223574689,2459868287, 43167...36781(34-digits),15171...11113(107-digits),46445...32211(129-digits), 28799...94029(530-digits), 59999...99999 (14564-digits) and many more added.

28 November, 2018:

• The page on Amazing Number 108 updated and enlarged.

• The page on Fascinating Triangular Numbers updated and enlarged.

• The page on Curious Properties of 153 updated and enlarged.

• The page on Amicable Numbers updated.

17 December, 2017:

• A new page on Amazing Number 108 added.

• The page on Fascinating Triangular Numbers updated and enlarged.

• DO YOU KNOW (25 October, 2006) Comments by Al Zimmermann given.

• DO YOU KNOW (30 October, 2016) Comments by Al Zimmermann given.

• Prime curios 5, 7, 216, 1333333 and 15423094826093 added.

30 October, 2016:

• CYF NO. 47 Solution by Bernard Fischel and Brian Trial given.

• CYF NO. 47 Comments by Selvam Chidambaram given.

• CYF NO. 41 Comments by K D Bajpai given.

• Prime curios 5, 853, 13579, 35333, 49019, 95063, 630745, 630745, 1110181, 1120573, 1180811, 1230127, 1440689, 2275327,2770513, 9040861, 14001019, 66410849, 101838101, 188303881, 396808693, 665067264, 968606869, 1023567948, 1124396857, 1124638579, 1124685973, 2547863419, 6650672647, 10123456897, 10123465789, 10124389567, 10125984763, 23457987601, 581321345589144233, 10591...10631(26 digit), 98761...13853(28 digit), 13171...17379 (34 digit), 17101...80291 (108 digit), 11111...11111 (109297 digit) and 11111...11111 (270343 digit) added.

4 November, 2015:

• The page on Fascinating Triangular Numbers updated and enlarged.

• CYF NO. 46 results by Al Zimmermann and Brian Trial given.

• CYF NO. 41 results by Brian Trial and Shyam Sunder Gupta given.

7 July, 2015:

• The page on Fascinating Triangular Numbers updated and enlarged.

• The page on Curious Properties of 153 updated.

• The page on Unique Numbers updated.

• CYF NO. 43 solution by Al Zimmermann given

• CYF NO. 26 Comments by Mauro Fiorentini given.

• CYF NO. 15 Comments by Mauro Fiorentini given.

• CYF NO. 7 Comments by Mauro Fiorentini given.

6 October, 2014:

• A new page on Fascinating Factorials added.

• CYF NO. 11 solution by David Harrison for a difficult and highly computational problem given.

• CYF NO. 44 solution by Fred Schneider given.

• CYF NO. 31 Comments by Paul Cleary given.

25 December, 2013:

• The page on Curious Properties of 153 updated.

• CYF NO. 38 Comments by Bernard Fischel given.

• Prime curios 13, 4369, 10301, 15709, 75353, 91019, 123191, 303593, 442619, 1120211, 336737123, 904719030, 1123564987, 13201010231, 16831813861, 1123529253211, 3842148274728412483, 3868168229228618683, 164471141292141174461 and 14422...32163 (24-digits) added.

15 July, 2013:

• The page on Fascinating Triangular Numbers enlarged.

• CYF NO. 42 Comments by Shyam Sunder Gupta given.

• CYF NO. 29 Comments by K D Bajpai given.

• CYF NO. 21 Solution by K D Bajpai, and Shyam Sunder Gupta given.

• Prime curios 311299, 353393243 and 49000...16941 (3742-digits) added.

13 November, 2012:

• The page on Unlucky 13 updated and enlarged.

• The page on Fascinating Triangular Numbers updated and enlarged.

• The page on Curious Properties of 153 updated.

• CYF NO. 40 contributions by Carlos Rivera, Maximilian Hasler, Brian Trial given.

• CYF NO. 29 Comments by - Mukesh Kr Jha given.

• CYF NO. 11 update by David Harrison given.

6 February, 2011:

• The page on Curious Properties of 153 updated.

• CYF NO. 40 contributions by B.S.Rangaswamy, Bo Gyu Jeong, Norman Luhn, Shyam Sunder Gupta given.

• CYF NO. 11 Comments by David Harrison given.

• Prime curios 19,101,449,12721,19891,12357321 and many others added.

• Integer Sequences A173542,A173543,A173544,A173545 added.

26 January, 2010:

• The page on Curious Properties of 153 updated

• Prime curios 61,67,168,173,227,349,353,378,431,434,701,729,948,1049,1471,1901,36563,60889 and many more added.

10 May, 2009:

• The page on Rare Numbers updated and enlarged. (List up to 10²⁰ )

• Prime curios 2311 and 23111...07673 (33-digits) added.

18 January, 2009:

• The page on Smith Numbers updated.

• CYF NO. 37 solutions by Luke Pebody , Jens Kruse Andersen, Donovan Johnson, Frederick Schneider given.

• CYF NO. 32 Comments by Luke Pebody given.

• Prime curios 313 and 95861...78973 (39-digits) added.

30 December, 2007:

• Integer Sequences A131306,A131316,A131535-A131552,A131604-A131606,A131609,
  A131612-A131618,A131620,A131625,A131627-A131630 added.

• CYF NO. 36 Solution by Luke Pebody, Bruno Mishutka given

14 July, 2007:

• Prime curios 4,17,1687,3283,91596...16721 (52-digits),23456...56789 (62-digits),78912...67891 (355-digits),79778...87797 (776-digits),12345...67891 (4690-digits),23456...89123 (4772-digits) added.

• CYF NO. 35 Solution by Jaroslaw Wroblewski, Frederick Schneider, Donovan Johnson given

26 January, 2007:

• The page on Cab Numbers added.

• CYF NO. 34 comments by Brian Trial, Nathan Gilbert given.

25 October, 2006:

• The page on Amicable Numbers updated.

• CYF NO. 33 solutions by Jens Kruse Andersen, Donovan Johnson, Carlos Rivera, Jacques Bernard, Nathan Gilbert, Gaurav Singh given.

• Prime curios 36,1135279341568,1311753223571113,17131175322357111317 added.

15 January, 2006:

• Prime curios 1267834459,5748693121,6913548721,12539670481,13069482857,17392546081 added.

• CYF NO. 32 Solution by Donovan Johnson given

7 November, 2005:

• The page on Amicable Numbers updated.

• CYF NO. 31 solutions by B.S.Rangaswamy, Brian Trial, Patrick De Geest given.

• Prime curios 23,41,191,1259,1291,22193,102251,3511973,4137473,5521819,5919931, 36101521,210231253,354963229,1914032047,171190210231, 19531891183017701711,18769...17689 (25-digits), 24649...25921 (25-digits) added.

1 May, 2005:

• The page on Smith Numbers updated.

• CYF NO. 30 comments by Norman Luhn given.

• Prime curios 827,6427,15131197,23252729,59575553,2527293133 and 2744337540964913 added.

11 March, 2005:

• New page on Smith Numbers added.

1 January, 2005:

• Prime curios 41,211,941,6481,235813,292319,59534743,3731292319,4916253649,576529484441,29313741434753,
  73727170696867,144121100816449,4847464544434241 and 841784729676625576529 added.

• CYF NO. 28 Solution by Jens Kruse Andersen and Donovan Johnson given.

• CYF NO. 21 Solution by Donovan Johnson

15 September, 2004:

• Prime curios 1,2,3,13,34,56,1801,5779 and many more added.

• CYF NO. 27 Solution by Carlos Rivera and Jens Kruse Andersen given.

• CYF NO. 1 Comments by Jens Kruse Andersen.

4 May, 2004:

• Prime curios 14,523,135979531,786655453628211510631 and many more added

2 March, 2004:

• CYF NO. 25 Solution by Jens Kruse Andersen (email dt 04-02-2004) and contributions by Serge Varjabedian and Patrick De Geest given.

• Prime curios 2,3,5,6,7,14,15,17,433,562,771,1049,2047,9041,65520,1235711,171311753,777...7573553 (100-digits),888...8081 (100-digits),10000...180181 (101-digits),10000...949 (101-digits),10000...2773 (101-digits),30000...3899 (101-digits),444...44969 (101-digits),777..73735353 (999-digits),8888...11101 (999-digits),10000...188001 (1000-digits),10000...18919 (1000-digits),10000...19411 (1000-digits),300..66833 (1000-digits) and many more added.

1 February, 2004:

• CYF NO. 24 Solution by Jens Kruse Andersen (email dt 02-01-2004) and Brian Trial (email dt 12-01-2004) given. Comments added.

• Prime curios 53,99999...99206 (100-digits),99999...99913 (100-digits),10000...00033 (101-digits),10000...00882 (101-digits),10000...00001 (101-digits),10000...00543 (601-digits),99999...94858 (999-digits),10000...05026 (1000-digits). added.

1 January, 2004:

• CYF NO. 23 Comments by Brian Trial (email dt 04-12-2003) added. Solution given.
• Prime curios 111,111111,2113665,11111111,111...111(12 digits),111...111(13 digits),111...111(15 digits),12345689798654321,111...111(32 digits),1000...00451(452 digits),1888...8881 (885 digits), 777..2..777(961 digits), 9888...8889(985 digits), 999..2..999 (1061 digits) added
• Page on Unlucky 13 updated.
• Page on Amicable Numbers updated.

8 November, 2003:

• Prime curios 36,227,353,626,949,13216141,509033161,10123456789,
  1023456798976543201 added

3 August, 2003:

• Prime curios 21,49,193,809,1009,2339,3793,5437,34273,101723,
  91439939,733929337,1123456987 added
• CYF NO. 20 Additional Comments by Jens Kruse Andersen (email dt 15-06-2003)

13 June, 2003:

• Page on Unlucky 13 updated.
• CYF NO. 20 Comments by Jens Kruse Andersen (email dt 24-05-2003)and Brian Trial (email dt 04-06-2003)

21 May, 2003:

• CYF NO. 19 Solved by Brian Trial (email dt 09-05-2003)
• CYF NO. 1 Comments by Phil Carmody (email dt 06-05-2003)
• CYF NO. 13 Comments by Adam Stinchcombe (email dt 05-05-2003)
• CYF NO. 17 Comments by Brian Trial (email dt 09-04-2003)

29 March, 2003:

• CYF NO. 18 Comments added. Almost solved.
• Prime curios 11,13,19,29,41,43,97,528,14269,16813...45651(507 digits),11151...11111 (666 digits), 99999...99999 (666 digits), 11111...11111 (999 digits), 99999...99999 (999 digits),11111...11111 (1000 digits),33333...33333(1000 digits) added

1 March, 2003:

• Prime curios 17,31,81,107,512,709,751,4713,5312,10000...00123 (666 digits),
  99999...98843 (666 digits), 10000... 26663 (1000 digits), 99999... 66007 (999 digits) added

1 February, 2003:

• CYF NO. 16 Solved by Jan Munch Pedersen and David Terr

1 January, 2003:

• CYF NO. 15 Solved by Brian Trial and Robin Suri

1 December, 2002:

• Page on Unlucky 13 updated.
• CYF NO. 14 Solved by Jens Kruse Andersen, Brian Trial and Robin Suri
• CYF NO. 12 Comments by Brian Trial (email dt 23-11-2002)
• CYF NO. 11 Comments by Paul Zimmermann (email dt 12-11-2002)

11 November, 2002:

• New page on My Favorite Books added.

• CYF NO. 13 Comments by Brian Trial (email dt 02-11-2002)
• CYF NO. 13 Comments by Jens Kruse Andersen (email dt 17-10-2002)

26 October, 2002:

• CYF NO. 8 Comments by Prof. François Bergeron (email dt 21-10-2002)

• A new page on Fascinating Triangular Numbers added.

5 October, 2002:

• CYF NO. 10 Solution by Brian Trial (email dt 04-10-2002)

• CYF NO.12 Results by Jens Kruse Andersen (email dt 25-09-2002)

21 September, 2002:

• CYF NO. 11 Comments by Patrick De Geest (email dt 17/18-09-2002)

• CYF NO.11 Results by Jens Kruse Andersen (email dt 18-09-2002)

6 September, 2002:

• CYF NO. 10 Comments by Brian Trial (email dt 14/25-06-2002)

• CYF NO.1 Results by Gerbicz Robert (email dt 08-07-2002)

• A new page on Smarandache Sequence of Happy Numbers added.

• Many Prime Curios added. For details see Prime Curios!

14 April, 2002:

• CYF NO. 9 Comments added . Almost Solved by Brian Trial. See Brian's Conjecture .
• Prime curios 5,19,29,207,220,567,1973,65281,112583,135799,206483,864203,975313,
  2024689,100123456789,198765432101 added

10 March, 2002:

• CYF NO. 8 Solved by Brian Trial
• CYF NO. 2 Comments added
• Prime curios 2,11,14,19,23,41,101,199,821,1297,4023,4201,6899,632148,19999999,
  191735161,1234457689,1608906624,3778888999,9876534120,10234465789,
  399899999999999,29998999999999999999999 added

17 February, 2002:

• CYF NO. 4 Solved by Carlos Rivera
• CYF NO. 7 Solved by Brian Trial
• CYF NO. 1 Comments added
• Prime curios 13,123456879,683441871,987634512,999828727,1023479856 added

10 February, 2002:

• The page on Curious Properties of 153 updated
• CYF NO. 1 & CYF NO. 2 Comments added
• Prime curios 27,140,726,3319,5879,6318,189375,211673,755968,118689518,179376463,202536181, 880346227 added

20 January, 2002:

• CYF NO. 6 Comments by Jan Munch Pedersen. He found that no solution exist for all known Amicable Numbers. (email dated 08-01-2002)
• The page on Amicable Numbers added

6 January, 2002:

• CYF NO. 5 Solved by Jan Munch Pedersen. He found that 6789783 is the smallest Odd Abundant Number not ending in 5 and also not divisible by 9. (email dated 03-01-2002)

31 December, 2001:

• The page on Curious Properties of 153 updated

25 December, 2001:

• The page on Curious Properties of 153 added

23 December, 2001:

• CYF NO. 3 Solved byPatrick De Geest. He found that n = 3088803 is the smallest multi-digit Palindromic number such that 10⁹⁹⁹ + n is prime.( email dt. 22-12-2001)

17 December, 2001:

• The page on Fascinating Squares added

9 December, 2001:

• The page on Unlucky 13 added

30 November, 2001:

• The list of all Rare Numbers up to 10^19 have been added.
• The page on Unique Numbers added

---------------------------------------------------------------------------------------------

Back Home