OFFSET
0,3
FORMULA
a(n) = sum_{k=0..floor(n/2)} ( sum_{j=0..n-k} C(2(n-2k), j)*C(2k, j)*2^j ).
Empirical g.f.: -(3*x^3+x^2+x-1) / ((x^3-3*x^2-x-1)*(x^3+x^2+3*x-1)). - Colin Barker, Sep 26 2014
MAPLE
A108478:=n->add(add(binomial(2*(n-2*k), j)*binomial(2*k, j)*2^j, j=0..n-k), k=0..floor(n/2)): seq(A108478(n), n=0..30); # Wesley Ivan Hurt, Sep 26 2014
MATHEMATICA
Table[Sum[Sum[Binomial[2 (n - 2 k), j]*Binomial[2 k, j]*2^j, {j, 0, n - k}], {k, 0, Floor[n/2]}], {n, 0, 30}] (* Wesley Ivan Hurt, Sep 26 2014 *)
PROG
(PARI) a(n) = sum(k=0, n\2, sum(j=0, n-k, binomial(2*(n-2*k), j)*binomial(2*k, j)*2^j)); \\ Michel Marcus, Sep 26 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jun 04 2005
STATUS
approved