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 A117542 #6 Feb 05 2014 20:18:18 %S A117542 1,2,6,8,36,16,127,320,581,1564,13565,13760,149186,773727,540538 %N A117542 Number of permutations P of 1..n such that in P and in the inverse of P, every pair of adjacent numbers and the first and last number, are relatively prime. %C A117542 Sequence suggested by _Leroy Quet_ on the SeqFan mailing list. %e A117542 a(4)=8, since the 8 permutations (1,2,3,4), (1,4,3,2), (2,1,4,3), (2,3,4,1), (4,1,2,3), (3,2,1,4), (3,4,1,2), (4,3,2,1) satisfy the property. %Y A117542 Cf. A076220, A117541. %K A117542 nonn %O A117542 1,2 %A A117542 _Giovanni Resta_, Mar 28 2006