A099216 a(n)=4a(n-1)-4a(n-2)+2a(n-3).

1, 2, 4, 10, 28, 80, 228, 648, 1840, 5224, 14832, 42112, 119568, 339488, 963904, 2736800, 7770560, 22062848, 62642752, 177860736, 504997632, 1433833088, 4071063296, 11558916096, 32819077376, 93182771712, 264572609536

Offset: 0

Author

Paul Barry, Oct 06 2004

Keywords

• easy
• nonn

Comments

Binomial transform of tribonacci numbers A000213.

Links

• Index entries for linear recurrences with constant coefficients, signature (4,-4,2).

Crossrefs

Cf. A099214, A099215, A055588.

Formula

G.f.: (1-2x)/((1-2x)^2-2x^3); a(n)=sum{k=0..floor(n/3), binomial(n-k, 2k)2^k*2^(n-3k)}.