A284716 Number of indecomposable permutations avoiding the pattern 2143.

1, 1, 3, 13, 63, 330, 1838, 10758, 65586, 413639, 2684469, 17852715, 121256457, 838843641, 5897455515, 42058344077, 303787163823, 2219452035639, 16383022072549, 122066094872139, 917245868993865, 6946236553301334, 52979616083094066, 406741647662973594

Offset

1,3

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..200

A. L. L. Gao, S. Kitaev, P. B. Zhang. On pattern avoiding indecomposable permutations, arXiv:1605.05490 [math.CO], 2016.

Formula

a(n) ~ 4 * 3^(2*n+1/2) / (Pi*n^4). - Vaclav Kotesovec, Apr 02 2017

Mathematica

Rest[CoefficientList[Series[2*x - 1 + (1-x)^2 * (1 + 5*x - (1-9*x)^(3/4) * (1-x)^(1/4) * HypergeometricPFQ[{-1/4, 3/4}, {1}, 64*x/((x-1)*(1-9*x)^3)])/(6*x^2), {x, 0, 30}], x]] (* Vaclav Kotesovec, Apr 02 2017 *)

Crossrefs

Sequence in context: A193112 A367061 A192729 * A107097 A202837 A370396

Adjacent sequences: A284713 A284714 A284715 * A284717 A284718 A284719

Keyword

nonn

Author

N. J. A. Sloane, Apr 02 2017

Extensions

More terms from Vaclav Kotesovec, Apr 02 2017

Status

approved