OFFSET
0,2
LINKS
FORMULA
a(n) = ((9 + sqrt(4))^n + (9 - sqrt(4))^n)/2.
From Philippe Deléham, Nov 26 2008: (Start)
a(n) = 18*a(n-1) - 77*a(n-2), n > 1; a(0)=1, a(1)=9.
G.f.: (1-9*x)/(1-18*x+77*x^2).
a(n) = (1/9^n)*Sum_{k=0..n} A098158(n,k)*9^(2*k)*4^(n-k). (End)
E.g.f.: exp(9*x)*cosh(2*x). - Elmo R. Oliveira, Aug 23 2024
EXAMPLE
a(3) = (11^3 + 7^3)/2 = 837.
PROG
(PARI) a(n)=(11^n+7^n)/2 \\ Charles R Greathouse IV, Aug 23 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Al Hakanson (hawkuu(AT)gmail.com), Nov 24 2008
EXTENSIONS
Extended beyond a(6) by Klaus Brockhaus, Nov 26 2008
More terms by Elmo R. Oliveira, Aug 23 2024
STATUS
approved