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 A361270 #20 Mar 08 2023 02:49:29 %S A361270 0,0,1,2,5,8,16,20,38,40,75,70,131,112,210,168,316,240,453,330,625, %T A361270 440,836,572,1090,728,1391,910,1743,1120,2150,1360,2616,1632,3145, %U A361270 1938,3741,2280,4408,2660,5150,3080,5971,3542,6875,4048,7866,4600,8948,5200,10125 %N A361270 Number of 1324-avoiding odd Grassmannian permutations of size n. %C A361270 A permutation is said to be Grassmannian if it has at most one descent. A permutation is odd if it has an odd number of inversions. %H A361270 Juan B. Gil and Jessica A. Tomasko, <a href="https://arxiv.org/abs/2207.12617">Pattern-avoiding even and odd Grassmannian permutations</a>, arXiv:2207.12617 [math.CO], 2022. %H A361270 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,0,-6,0,4,0,-1). %F A361270 G.f.: x^2*(2*x^4+x^2+2*x+1)/((1+x)^4*(1-x)^4). %e A361270 For n=4 the a(4)=5 permutations are 1243, 2134, 2341, 2413, 4123. %o A361270 (PARI) Vec(x^2*(2*x^4+x^2+2*x+1)/((1+x)^4*(1-x)^4)+O(x^50)) \\ _Michel Marcus_, Mar 07 2023 %Y A361270 Cf. A356185, A361271. %K A361270 nonn,easy %O A361270 0,4 %A A361270 _Juan B. Gil_, Mar 07 2023