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 A373115 #12 May 25 2024 16:17:23 %S A373115 1,0,0,1,35,1661,107002,9047970,972937247,129603346139,20934881571217, %T A373115 4029204458109445,910549073414709876,238643240329544375336, %U A373115 71772700696174395158056,24544642886642172762170933,9468192975202745545226891834,4090995487728206638560153282674 %N A373115 Number weak ascent sequences of length 2n (prefixed with a zero) with exactly n weak ascents. %H A373115 Alois P. Heinz, <a href="/A373115/b373115.txt">Table of n, a(n) for n = 0..70</a> %H A373115 Beata Benyi, Anders Claesson, and Mark Dukes, <a href="https://arxiv.org/abs/2111.03159">Weak ascent sequences and related combinatorial structures</a>, arXiv:2111.03159 [math.CO], 2021-2022. %F A373115 a(n) = A369321(2n,n). %p A373115 b:= proc(n, i, t) option remember; expand(`if`(n=0, 1, add( %p A373115 b(n-1, j, t+`if`(j>=i, 1, 0))*`if`(j>=i, x, 1), j=0..t+1))) %p A373115 end: %p A373115 a:= n-> coeff(b(2*n, -1$2), x, n): %p A373115 seq(a(n), n=0..17); %Y A373115 Cf. A357141, A369321. %K A373115 nonn %O A373115 0,5 %A A373115 _Alois P. Heinz_, May 25 2024