OFFSET
0,2
COMMENTS
Diagonal sums of number triangle A106187.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
FORMULA
G.f. 1 / ((1 - x^2) * sqrt(1 - 4*x)).
a(n)=sum{k=0..floor(n/2), binomial(2(n-2k), n-2k)}.
PSUMSIGN transform of A006134. a(n+1) + a(n) = A006134(n). a(n) = Sum_{k=0..n} (-1)^k * binomial(2 * (n-k), n-k). - Michael Somos, Jun 20 2012
D-finite with recurrence: n*a(n)+2*(1-2*n)*a(n-1) -n*a(n-2) +2*(2*n-1)*a(n-3)=0. - R. J. Mathar, Nov 09 2012
a(n) ~ 2^(2*n+4) / (15*sqrt(Pi*n)). - Vaclav Kotesovec, Feb 03 2014
EXAMPLE
1 + 2*x + 7*x^2 + 22*x^3 + 77*x^4 + 274*x^5 + 1001*x^6 + 3706*x^7 + 13871*x^8 + ...
MATHEMATICA
CoefficientList[Series[1/((1-x^2)*Sqrt[1-4*x]), {x, 0, 20}], x] (* Vaclav Kotesovec, Feb 03 2014 *)
PROG
(PARI) x='x+O('x^50); Vec(1/((1-x^2)*sqrt(1-4*x))) \\ G. C. Greubel, Mar 16 2017
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Apr 24 2005
STATUS
approved