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 A369626 #15 Feb 25 2024 00:32:10 %S A369626 1,1,2,6,21,75,265,925,3201,11017,37793,129393,442497,1512225,5165953, %T A369626 17643457,60250113,205729921,702452225,2398414593,8188884993 %N A369626 a(n) is the number of permutations of [n] which avoid the patterns 1234, 1324, and 2413. %e A369626 All 6 of the permutations of length 3 avoid all patterns of length 4, so a(3)=6. %Y A369626 Cf. A033321 (avoiding 1234, 1324, and 1342), A369431 (avoiding 1234, 1324, 1342, and 2413). %K A369626 nonn,more %O A369626 0,3 %A A369626 _Matt Slattery-Holmes_, Feb 05 2024 %E A369626 a(11)-a(20) from _Martin Ehrenstein_, Feb 24 2024