OFFSET
0,3
COMMENTS
Hankel transform of a(n+1) is A136577 (conjecture).
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: (sqrt(1+4*x-4*x^2)+4*x^2-2*x-1)/(8*x^2).
Conjecture: (n+2)*a(n) + 2*(2*n+1)*a(n-1) + 4*(1-n)*a(n-2) = 0. - R. J. Mathar, Dec 11 2011
a(n) ~ (-1)^(n+1) * (3+2*sqrt(2)) * sqrt(4-2*sqrt(2)) * 2^(n-2) * (1+sqrt(2))^n / (sqrt(Pi) * n^(3/2)). - Vaclav Kotesovec, Jan 22 2014
For n >= 1, a(n) = (-1)^(n+1) * (1/2) * A071356(n) = (-1)^(n+1) * Sum_{k = 0..floor(n/2)} binomial(n, 2*k)*Catalan(k)*2^(n-k-1). The recurrence given above follows from this using the WZ algorithm. - Peter Bala, Apr 28 2024
MATHEMATICA
CoefficientList[Series[(Sqrt[1+4*x-4*x^2]+4*x^2-2*x-1)/(8*x^2), {x, 0, 20}], x] (* Vaclav Kotesovec, Jan 22 2014 *)
PROG
(PARI) x='x+O('x^50); concat([0], Vec((sqrt(1+4*x-4*x^2)+4*x^2-2*x-1)/(8*x^2))) \\ G. C. Greubel, Mar 21 2017
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Jan 08 2008
STATUS
approved