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 A274997 #33 Dec 11 2016 11:43:29 %S A274997 0,0,0,1,6,41,274,2040,16346,143571,1365354,14056287,155638724, %T A274997 1847352720,23400880036,315270938501,4502081195166,67941159822229, %U A274997 1080528172834710,18065046986905320,316769071197428286,5813469963339136855,111449225620923739458 %N A274997 Number of permutations of [n] having exactly one doubledescent. %H A274997 Alois P. Heinz, <a href="/A274997/b274997.txt">Table of n, a(n) for n = 0..463</a> %F A274997 a(n) ~ c * 3^(3*n/2) * n^(n+3/2) / (exp(n) * 2^n * Pi^n), where c = 0.827206526063705458546024... . - _Vaclav Kotesovec_, Dec 11 2016 %Y A274997 Column k=1 of A162975. %K A274997 nonn %O A274997 0,5 %A A274997 _Alois P. Heinz_, Nov 29 2016