SPOILER C: - - - - - - - - - - - - - - - - - - - - - - - - - - - ==> arithmetic/digits/squares/three.digits.s <== puzzles-faq/part03 What square consits entirely of three digits (e.g. 2, 4, and 8) ? 4, 484, 28224, 228484, 8282884, 44484284288828484, ... Ref: - Ilan Vardi, Computational Recreations in Mathematica, Chapter 2. Exercise 2.2 (a Mathematica is given) The independence heuristic says: the series is finite.