OFFSET
1,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
A. L. L. Gao, S. Kitaev, P. B. Zhang. On pattern avoiding indecomposable permutations, arXiv:1605.05490 [math.CO], 2016.
FORMULA
G.f.: (1/2)*(sqrt(1-4*x) + 1) * (32*x/(1 + 20*x - 8*x^2 - (1-8*x)^(3/2)) - 1) [Gao, Kitaev and Zhang]. - Vaclav Kotesovec, Apr 02 2017
a(n) ~ (2+sqrt(2)) * 2^(3*n+4) / (243*sqrt(Pi)*n^(5/2)). - Vaclav Kotesovec, Apr 02 2017
MATHEMATICA
Rest[CoefficientList[Series[1/2*(Sqrt[1 - 4*x] + 1)*(32*x/(1 + 20*x - 8*x^2 - (1 - 8*x)^(3/2)) - 1), {x, 0, 20}], x]] (* Vaclav Kotesovec, Apr 02 2017 *)
PROG
(Magma) m:=30; R<x>:=LaurentSeriesRing(RationalField(), m); Coefficients(R!(((1/2*(Sqrt(1-4*x)+1)*(32*x/(1+20*x-8*x^2- (1-8*x)^(3/2))-1))))); // Vincenzo Librandi, Apr 04 2017
(PARI) x='x+O('x^50); Vec((1/2)*(sqrt(1-4*x) + 1) * (32*x/(1 + 20*x - 8*x^2 - (1-8*x)^(3/2)) - 1)) \\ G. C. Greubel, Apr 11 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Apr 02 2017
EXTENSIONS
More terms from Vaclav Kotesovec, Apr 02 2017
STATUS
approved