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A284712
Number of indecomposable permutations avoiding the pattern 4321.
1
1, 1, 3, 12, 56, 289, 1603, 9391, 57437, 363773, 2371551, 15842850, 108070370, 750655459, 5297314241, 37909476912, 274693258884, 2012767854337, 14897269924571, 111269729060260, 838012360130944, 6359434553977763, 48597188639038769, 373757879279966501
OFFSET
1,3
LINKS
A. L. L. Gao, S. Kitaev, P. B. Zhang. On pattern avoiding indecomposable permutations, arXiv:1605.05490 [math.CO], 2016.
FORMULA
a(n) ~ c * 3^(2*n) / n^4, where c = 2.102569600767282153... . - Vaclav Kotesovec, Apr 03 2017
MATHEMATICA
Rest[CoefficientList[Series[1 - 6*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)]), {x, 0, 30}], x]] (* Vaclav Kotesovec, Apr 03 2017 *)
CROSSREFS
Sequence in context: A224922 A303925 A215252 * A284713 A180256 A369600
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 02 2017
EXTENSIONS
More terms from Vaclav Kotesovec, Apr 03 2017
STATUS
approved