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 A171808 #5 Mar 30 2020 15:18:12 %S A171808 1,15,20,0,24 %N A171808 Number of 5 X 5 permutation matrices such that the n-th matrix power is the identity matrix and the determinant is +1. %C A171808 Sum of this sequence is equal to the number of permutation matrices with determinant +1 = 5!/2 = 60. For number matrices with determinant = -1 see A171809. %e A171808 a(1)=1 because there is only one matrix whose first power is the identity matrix (this is the identity matrix itself). %Y A171808 Cf. A171806, A171809. %K A171808 fini,nonn,full %O A171808 1,2 %A A171808 _Artur Jasinski_, Dec 18 2009