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 A111280 #27 Mar 12 2024 08:51:13
%S A111280 1,1,2,6,22,113,431,1584,5920,22214,83239,311777,1167902,4375090,
%T A111280 16389450,61395989,229993639,861572476,3227511492,12090486122,
%U A111280 45291815419,169666341761,635582108218,2380935499534,8919152662622,33411776268873
%N A111280 Number of permutations avoiding the patterns {4231, 4321, 35142, 45312, 42513, 45132, 35412, 45213, 43512, 456123, 351624, 451623, 356124}; number of strong sorting class based on 4231.
%H A111280 M. Albert, R. Aldred, M. Atkinson, C Handley, D. Holton, D. McCaughan and H. van Ditmarsch, <a href="https://doi.org/10.37236/1928">Sorting Classes</a>, Elec. J. of Comb., Vol. 12 (2005), R31.
%H A111280 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (4,-2,4,0,-1).
%F A111280 a(n) = 4*a(n-1)-2*a(n-2)+4*a(n-3)-a(n-5).
%F A111280 G.f.: 1+x*(1-2*x-2*x^3+29*x^4)/(1-4*x+2*x^2-4*x^3+x^5). - _Colin Barker_, Jan 16 2012
%t A111280 a[1] = 1; a[2] = 2; a[3] = 6; a[4] = 22; a[5] = 113; a[n_] := a[n] = 4a[n - 1] - 2a[n - 2] + 4a[n - 3] - a[n - 5]; Table[ a[n], {n, 25}] (* _Robert G. Wilson v_, Nov 04 2005 *)
%t A111280 LinearRecurrence[{4,-2,4,0,-1},{1,2,6,22,113},30] (* _Harvey P. Dale_, Jun 03 2019 *)
%K A111280 nonn,easy
%O A111280 0,3
%A A111280 _Len Smiley_, Nov 01 2005
%E A111280 More terms from _Robert G. Wilson v_, Nov 04 2005
%E A111280 a(0)=1 prepended by _Alois P. Heinz_, Mar 12 2024