A097335 a(n) = Sum_{k=0..n} C(n-k, floor(k/2))*3^k.

1, 4, 4, 13, 49, 85, 202, 643, 1408, 3226, 9013, 21685, 50719, 131836, 327001, 783472, 1969996, 4913005, 11964253, 29694217, 73911262, 181589539, 448837492, 1114038850, 2748344701, 6787882129, 16814231779, 41549334088, 102640273249

Offset: 0

Author

Paul Barry, Aug 05 2004

Keywords

• easy
• nonn

Links

• Index entries for linear recurrences with constant coefficients, signature (1,0,9)

Crossrefs

Cf. A097333, A097334, A097336.

Formula

G.f. : (1+3x)/(1-x-9x^3); a(n)=a(n-1)+9a(n-3).