This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181580 #6 Sep 01 2013 22:35:40 %S A181580 2,5,11,17,23,0,29,31,37,41,47,0,53,59,61,67,71,0,79,83,89,0,97,0,101, %T A181580 107,113,0,0,0,0,127,131,137,0,149,0,151,157,163,167,173,0,179,181,0, %U A181580 191,197,0,0,0,211,0,223,0,227,233,239,241,0,0,0,251,257,263,269,271,0 %N A181580 Smallest prime p such that p! ends with exactly n trailing 0's (or 0, if no such p exists). %e A181580 For any positive integer n, n! must have at least as many trailing 0's as does (n-1)!; thus, other than the terms where a(n)=0, the sequence is strictly increasing. %e A181580 2 is the first prime whose factorial (2! = 2) has no trailing 0's, so a(0)=2. %e A181580 5 is the first prime whose factorial (5! = 120) has one trailing 0, so a(1)=5. %e A181580 There is no number whose factorial has exactly 5 trailing 0's (since the factorials of 24 and 25 have 4 and 6 trailing 0's, respectively), so a(5)=0. %Y A181580 Cf. A181579 %K A181580 nonn,base %O A181580 0,1 %A A181580 _Lekraj Beedassy_, Nov 02 2010