A133594 a(n)=3*a(n-1)+12*a(n-2) for n>=3, a(0)=1, a(1)=3, a(2)=18 .

1, 3, 18, 90, 486, 2538, 13446, 70794, 373734, 1970730, 10396998, 54839754, 289283238, 1525926762, 8049179142, 42458658570, 223966125414, 1181402279082, 6231800342214, 32872228375626, 173398289233446, 914661608207850

Offset: 0

Author

Philippe Deléham, Dec 31 2007

Keywords

• easy
• nonn

Links

• Index entries for linear recurrences with constant coefficients, signature (3,12).

Programs

Mathematica

LinearRecurrence[{3,12},{1,3,18},30] (* Harvey P. Dale, Dec 20 2020 *)

Formula

G.f.: (1-3*x^2)/(1-3*x-12*x^2) . a(n) = Sum_{k, 0<=k<=n}A122950(n,k)*3^k .