A113312 Expansion of (1+x)^2/(1-2x^2+x^3).

1, 2, 3, 3, 4, 3, 5, 2, 7, -1, 12, -9, 25, -30, 59, -85, 148, -229, 381, -606, 991, -1593, 2588, -4177, 6769, -10942, 17715, -28653, 46372, -75021, 121397, -196414, 317815, -514225, 832044, -1346265, 2178313, -3524574, 5702891, -9227461, 14930356, -24157813, 39088173, -63245982, 102334159

Offset: 0

Author

Paul Barry, Oct 25 2005

Keywords

• easy
• sign

Comments

Diagonal sums of A113310.

Links

• Index entries for linear recurrences with constant coefficients, signature (0, 2, -1).

Programs

Mathematica

LinearRecurrence[{0,2,-1},{1,2,3},50] (* Harvey P. Dale, May 19 2014 *)

Formula

a(n)=2a(n-2)-a(n-3); a(n)=sum{k=0..floor(n/2), sum{i=0..n-2k, (-1)^i*C(i+k-2, i)}}.