OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
J. L. Baril, Avoiding patterns in irreducible permutations, Discrete Mathematics and Theoretical Computer Science, submitted 2014. See Table 3.
FORMULA
a(n) ~ 2^(2*n+2) / (9*sqrt(Pi*n)). - Vaclav Kotesovec, Nov 10 2016
Conjecture: +n*(3*n^2-12*n+11) *a(n) -(3*n-5) *(3*n^2-9*n+4) *a(n-1) -2*(2*n-5) *(3*n^2-6*n+2) *a(n-2) +n *(3*n^2-12*n+11) *a(n-3) -2 *(2*n-5) *(3*n^2-6*n+2) *a(n-4)=0. - R. J. Mathar, Jun 24 2018
MATHEMATICA
CoefficientList[Series[2*x*(1-x*Sqrt[1-4*x])/(Sqrt[1-4*x]*(1+2*x^2+Sqrt[1-4*x])), {x, 0, 20}], x] (* Vaclav Kotesovec, Nov 10 2016 *)
PROG
(PARI) x='x+O('x^50); concat([0], Vec(2*x*(1-x*sqrt(1-4*x) )/( (1+ 2*x^2 +sqrt(1-4*x))*sqrt(1-4*x)))) \\ G. C. Greubel, Jun 05 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 09 2016
STATUS
approved