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) ~ 3^(2*n+7/2) * phi^2 / (16*Pi*n^4), where phi = A001622 = (1+sqrt(5))/2 is the golden ratio. - Vaclav Kotesovec, Apr 02 2017
MATHEMATICA
Rest[CoefficientList[Series[1/2*(Sqrt[1-4*x] + 1)*((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) - 1), {x, 0, 30}], x]] (* Vaclav Kotesovec, Apr 02 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 02 2017
EXTENSIONS
More terms from Vaclav Kotesovec, Apr 02 2017
STATUS
approved