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 A383771 #13 May 14 2025 00:18:56 %S A383771 1,1,4,19,102,590,3588,22617,146460,968520,6513034,44403604,306209746, %T A383771 2132165062,14970030506,105862919427,753344866662,5390772814578, %U A383771 38765692377100,279999861952626,2030439981144348,14776796428607224,107891287190000212,790105506941871258 %N A383771 Number of noncrossing permutations of [n] avoiding 213 (and by symmetry 132, 213, or 312). %H A383771 K. Archer and R. P. Laudone, <a href="https://arxiv.org/abs/2502.13309">Pattern avoidance in non-crossing and non-nesting permutations</a>, arXiv:2502.13309 [math.CO], 2025. %F A383771 G.f.: A(x) satisfies x^2*A(x)^4 - (x^2+x)*A(x)^3 - x*A(x)^2 + (x+1)*A(x) - 1 = 0. %Y A383771 Cf. A383770. %K A383771 nonn %O A383771 0,3 %A A383771 _Robert P. Laudone_, May 09 2025