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F(1998)

Source: Cono Sur Olympiad, Uruguay 1989, Problem#3

May 14, 2006
function

Problem Statement

A number pp is perfectperfect if the sum of its divisors, except pp is pp. Let ff be a function such that: f(n)=0f(n)=0, if n is perfect f(n)=0f(n)=0, if the last digit of n is 4 f(a.b)=f(a)+f(b)f(a.b)=f(a)+f(b) Find f(1998)f(1998)
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