99868...86899 (25-digits)

This number is a composite.

                                                 99868 3178136263 1871386899

The semiprime 9986831781362631871386899 = 2048903657 * 4874232005610907 is the largest of the 203 positive integers N such that for some integer d => 2 this number is a d-digit palindrome base 10 as well as a d-digit palindrome for some base b different from 10. Curiously, the smallest such integer, 22, and the number of solutions 203 = 7 * 29, are also semiprimes. [Post]