CMO 1989 Problem 3

Define $\{ a_n \}_{n=1}$ as follows: $a_1 = 1989^{1989}; \ a_n, n > 1,$ is the sum of the digits of $a_{n-1}$ . What is the value of $a_5$ ?

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.