OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: A(x)=Sqrt((1-x)/(1+7x)).
From Seiichi Manyama, Feb 03 2023: (Start)
a(n) = Sum_{k=0..n} (-2)^k * binomial(n-1,n-k) * binomial(2*k,k).
n*a(n) = -2*(3*n-1)*a(n-1) + 7*(n-2)*a(n-2). (End)
MATHEMATICA
CoefficientList[Series[Sqrt[(1-x)/(1+7 x)], {x, 0, 30}], x]
PROG
(PARI) a(n) = sum(k=0, n, (-2)^k*binomial(n-1, n-k)*binomial(2*k, k)); \\ Seiichi Manyama, Feb 03 2023
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Mario Catalani (mario.catalani(AT)unito.it), Jul 01 2003
STATUS
approved