Triangle read by rows: T(n,k) is the number of permutations pi of [n] such that pi has k descents and s(pi) avoids the patterns 132 and 321, where s is West's stack-sorting map (0 <= k <= n-1).
A319029
Triangle read by rows: T(n,k) is the number of permutations pi of [n] such that pi has k descents and s(pi) avoids the patterns 132 and 321, where s is West's stack-sorting map (0 <= k <= n-1).
Terms
- a(0) =1a(1) =1a(2) =1a(3) =1a(4) =4a(5) =1a(6) =1a(7) =10a(8) =10a(9) =1a(10) =1a(11) =20a(12) =46a(13) =20a(14) =1a(15) =1a(16) =35a(17) =146a(18) =146a(19) =35a(20) =1a(21) =1a(22) =56a(23) =371a(24) =666a(25) =371a(26) =56a(27) =1a(28) =1a(29) =84
External references
- oeis: A319029