This article is from the Puzzles FAQ, by Chris Cole firstname.lastname@example.org and Matthew Daly email@example.com with numerous contributions by others.
Is it possible to form two numbers A and B from 22 digits such that
A = B^2? Of course, leading digits must be non-zero.
No, the number of digits of A^2 must be of the form 3n or 3n-1.