A133681 a(n)=9*a(n-1)+90*a(n-2) for n>=3, a(0)=1, a(1)=9, a(2)=162 .

1, 9, 162, 2268, 34992, 519048, 7820712, 117100728, 1757770632, 26359001208, 395430367752, 5931183418488, 88969383864072, 1334530962440568, 20018023209731592, 300269995507235448, 4504052048440962312

Offset: 0

Author

Philippe Deléham, Dec 31 2007

Keywords

• easy
• nonn

Formula

G.f.: (1-9*x^2)/(1-9*x-90*x^2) . a(n) = Sum_{k, 0<=k<=n}A122950(n,k)*9^k .