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 A320957 #9 Aug 19 2021 11:04:19
%S A320957 1,1,2,10,70,656,7442,99280,1515190,26038016,497227682,10445708800,
%T A320957 239394707110,5943715352576,158922998335922,4552807055288320,
%U A320957 139123511874743830,4517007538261262336,155283277843358756162,5634815061983539363840,215234080472925069593350
%N A320957 a(n) = (1/6)*n!*[x^n] (2 + sec(3*x) + tan(3*x) + 3*sec(x) + 3*tan(x)).
%C A320957 See A320956 for motivation and definitions.
%p A320957 egf := 2 + sec(3*x) + tan(3*x) + 3*sec(x) + 3*tan(x):
%p A320957 ser := series(egf, x, 22): seq((1/6)*n!*coeff(ser, x, n), n=0..20);
%t A320957 m = 20;
%t A320957 egf = 2 + Sec[3x] + Tan[3x] + 3 Sec[x] + 3 Tan[x];
%t A320957 (1/6) CoefficientList[egf + O[x]^(m+1), x] Range[0, m]! (* _Jean-François Alcover_, Aug 19 2021 *)
%o A320957 (PARI) sectan(x) = 1/cos(x) + tan(x);
%o A320957 my(x='x+O('x^25)); Vec(serlaplace(2 + sectan(3*x) + 3*sectan(x)))/6 \\ _Michel Marcus_, Aug 19 2021
%Y A320957 Cf. A000111 (n=1), A000828 (n=2), this sequence (n=3), A321394 (n=4), A320956.
%K A320957 nonn
%O A320957 0,3
%A A320957 _Peter Luschny_, Nov 08 2018