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 A182540 #25 Sep 08 2013 11:22:54 %S A182540 0,0,0,0,0,1,6,44,208,912,8016,61952,671248,8160620,87412258, %T A182540 888954284,12156253488,180955852060,2907927356451,50317255621843, %U A182540 802326797235038,12251146829850324,233309934271940028,4243527581615332664,79533825261873435894,1602629887788636447221,30450585799991840921483,622433536382831426225696,14891218890120375419560713,344515231090957672408413959 %N A182540 Number of ways of arranging the numbers 1 through n on a circle so that no sum of two adjacent numbers is prime, up to rotations and reflections. %e A182540 If n < 6, then in every arrangement of the numbers 1 through n on a circle, there are two adjacent numbers adding up to a prime. For n = 6, the only arrangement without a prime sum is (1, 3, 6, 2, 4, 5). %Y A182540 Cf. A051252, A073452, A191374 %K A182540 nonn %O A182540 1,7 %A A182540 _Jens Voß_, May 04 2012 %E A182540 a(15)-a(17) from _Alois P. Heinz_, May 04 2012 %E A182540 a(18) from _R. H. Hardin_, May 07 2012 %E A182540 a(19)-a(30) from _Max Alekseyev_, Aug 19 2013