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 A171809 #2 Mar 31 2012 10:22:15 %S A171809 0,10,0,30,0,20 %N A171809 Number of 5 X 5 permutation matrices such that the n-th matrix power is the identity matrix and the determinant is -1. %Y A171809 Cf. A171806, A171808 %K A171809 fini,nonn,full %O A171809 1,2 %A A171809 _Artur Jasinski_, Dec 18 2009, corrected Dec 28 2009