ÖMO 1999 Problem 1

Prove that for each positive integer $n$ , the sum of the numbers of digits of $4^n$ and of $25^n$ (in the decimal system) is odd.

Dataset text AI-MO AoPS. Quoted with source.

Solutions

No solution is on olymmath yet. Official and human solutions come first when they arrive. AI solutions come after them, with a label.