A positive integer T is defined as a factorial tail if there exists a positive integer P such that the decimal expansion of P! ends with precisely T consecutive zeroes, and (T+1)^th digit from the right in P! is nonzero.

How many positive integers less than 1992 are not factorial tails?

(In reply to Complete Analytic Solution by Jer)

"The first thing we need is the largest factorial with 1992 zeroes or fewer."

That would be 7984!. What was found was 7980!, which is the smallest factorial with 1992 terminal zeros or more.

Posted by Charlie on 2009-02-25 11:19:14