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 A249392 #14 Mar 08 2024 18:13:33 %S A249392 1,1,0,0,0,0,0,0,0,0,1,32,1088,17280,293832,4004352,57687080, %T A249392 773838336,10900027949,151388845568,2200665880514,32321771402240, %U A249392 495575856116168,7760560549644288,126552637539515688 %N A249392 The number of down-up permutations of [n] where adjacent elements differ by at least 5. %Y A249392 Cf. A245377 (at least 2), A249390 (at least 3), A249391 (at least 4), A249393 (at least 6), A179958 (non-alternating) %K A249392 nonn,more %O A249392 0,12 %A A249392 _R. J. Mathar_, Oct 27 2014 %E A249392 a(17)-a(21) from _Alois P. Heinz_, Oct 27 2014 %E A249392 a(22)-a(24) from _Max Alekseyev_, Feb 24 2024