Number Recreations

Shyam Sunder Gupta
Director(Railways and Metros),
Consulting Engineers Group, Jaipur, India-302017

What is New? (Update 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,
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

Do You Know?

The digital root of product of twin primes other than (3,5) is always 8.

Can You Find?

CYF NO. 51
The smallest titanic Sphenic number (i.e. products of 3 distinct primes).

email your answer


Note: The above topics including many more will be added in due course.


My Contributions in Prime Curios

Prime Curios! - site maintained by G. L. Honaker Jr. and Chris Caldwell

My Favorite Links

  • Magic Squares,Magic Stars and Other Interesting number patterns by Harvey Heinz
  • Mudd Math Fun Facts pages
  • On-Line Encyclopedia of Integer Sequences OEIS
  • Math Puzzles
    An interesting site with lot of math recreations by Ed Pegg Jr.

My Favorite Books

Recommended list of books for those interested in Recreational and Computational Number theory
In Association with In Association with

The Rail
(January, 2003)

(March, 2003)
The Busy Educator Award
(October, 2003)

Send me e-mail at

This page was last updated on 15th September, 2019.

Copyright 2001-2019 Shyam Sunder Gupta. All rights reserved.