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 A361274 #9 Mar 10 2023 09:11:06
%S A361274 1,1,1,3,5,12,17,32,41,67,81,121,141,198,225,302,337,437,481,607,661,
%T A361274 816,881,1068,1145,1367,1457,1717,1821,2122,2241,2586,2721,3113,3265,
%U A361274 3707,3877,4372,4561,5112,5321,5931,6161,6833,7085,7822,8097,8902,9201,10077,10401
%N A361274 Number of 1342-avoiding even Grassmannian permutations of size n.
%C A361274 A permutation is said to be Grassmannian if it has at most one descent. A permutation is even if it has an even number of inversions.
%C A361274 a(n) is also the number of 3124-avoiding even Grassmannian permutations of size n.
%H A361274 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 A361274 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,3,-3,-3,3,1,-1).
%F A361274 G.f.: -(2*x^6-x^5-5*x^4-2*x^3+3*x^2-1)/((x+1)^3*(x-1)^4).
%F A361274 E.g.f.: ((24 - 9*x + 6*x^2 + 2*x^3)*cosh(x) + (33 - 6*x + 9*x^2 + 2*x^3)*sinh(x))/24. - _Stefano Spezia_, Mar 09 2023
%e A361274 For n=4 the a(4) = 5 permutations are 1234, 1423, 2314, 3124, 3412.
%t A361274 LinearRecurrence[{1,3,-3,-3,3,1,-1},{1,1,1,3,5,12,17},51] (* _Stefano Spezia_, Mar 09 2023 *)
%Y A361274 Cf. A356185, A361271.
%K A361274 nonn,easy
%O A361274 0,4
%A A361274 _Juan B. Gil_, Mar 09 2023