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 re(2): Computer Solution by Charlie)

after seeing your posts I reevaluated my computations and I agree with your soultions.  I got my solution by making an erroneous assumption about the differences between each consecutive non-factorial tail number.  While most of the differences are in fact 6 as I orignally assumed there is a differnence of 1 every 6'th difference and that caused the error in my computation of the total number.

Posted by Daniel on 2009-02-23 13:10:46