A131298 Diagonal sums of A104730.

1, 1, 2, 4, 6, 11, 18, 30, 50, 82, 135, 221, 361, 589, 959, 1560, 2535, 4116, 6679, 10832, 17560, 28457, 46103, 74674, 120928, 195802, 316995, 513148, 830608, 1344372, 2175796, 3521249, 5698477

Offset: 0

Author

Paul Barry, Jun 26 2007

Keywords

• easy
• nonn

Links

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

Crossrefs

Cf. A104730.

Programs

Mathematica

LinearRecurrence[{1,2,0,-2,-1},{1,1,2,4,6},40] (* Harvey P. Dale, Aug 21 2021 *)

Formula

G.f.: (1-x^2)/((1-x-x^2)*(1-x^2-x^3)) = (1+x)/(1-x-x^2) - x*(1+x)/(1-x^2-x^3).

a(n) = Sum_{k=0..floor(n/2)} C(n-k+1,k) - C(k,n-2k+1).