Sum of the Digit Sequence
Source: CMO 1989 #3
July 31, 2008
modular arithmeticlogarithmsalgebrabinomial theoremnumber theorydivisibility tests
Problem Statement
Define \{ a_n \}_{n\equal{}1} as follows: a_1 \equal{} 1989^{1989}; \ a_n, n > 1, is the sum of the digits of a_{n\minus{}1}. What is the value of ?