OFFSET
0,2
COMMENTS
For positive n, a(n) equals 4^n times the permanent of the (2n) X (2n) matrix with 1/2's along the main diagonal, and i's along the superdiagonal and the subdiagonal (where i is the imaginary unit). - John M. Campbell, Jul 08 2011
LINKS
FORMULA
G.f.: (1 + 4*x)/(1 + 7*x + 16*x^2).
a(n) = -7*a(n-1) - 16*a(n-2), a(0)=1, a(1)=-3.
a(n) = Sum_{k=0..n} binomial(n+k,2*k)*(-4)^(n-k).
MATHEMATICA
CoefficientList[Series[(1 + 4x)/(16x^2 + 7x + 1), {x, 0, 25}], x]
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Mario Catalani (mario.catalani(AT)unito.it), Aug 22 2003
STATUS
approved