The 196-algorithm consists of taking any positive integer of two digits or more, reversing the digits, and adding to the original number. The 196-algorithm termination problem then asks if iterating this procedure starting with the number 196 eventually produces a palindromic number.

status | open

The first few numbers not known to produce palindromes are 196, 295, 394, 493, 592, 689, 691, 788, 790, 879, 887, .... As of 1995, Tim Irvin halted iteration without encountering a palindrome after reaching a 2, 000, 000-digit number. As of May 2006, VanLandingham halted without encountering a palindrome after 724, 756, 966 iterations, reaching a number with more than 300 million digits.

mathematical problems | unsolved mathematics problems