A099214 a(n)=4a(n-1)-4a(n-2)+4a(n-3).

1, 2, 4, 12, 40, 128, 400, 1248, 3904, 12224, 38272, 119808, 375040, 1174016, 3675136, 11504640, 36014080, 112738304, 352915456, 1104764928, 3458351104, 10826006528, 33889681408, 106088103936, 332097716224, 1039597174784

Offset: 0

Author

Paul Barry, Oct 06 2004

Keywords

• easy
• nonn

Comments

Binomial transform of A099213.

Crossrefs

Cf. A073724.

Formula

G.f.: (1-2x)/((1-2x)^2-4x^3); a(n)=sum{k=0..floor(n/3), binomial(n-k, 2k)4^k*2^(n-3k)}.