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A152106
a(n) = (11^n + 7^n)/2.
1
1, 9, 85, 837, 8521, 88929, 944605, 10155357, 110061841, 1199150649, 13109949925, 143644498677, 1576134831961, 17309800577169, 190214028328045, 2090997865462797, 22991481397070881, 252839829506640489, 2780772863545070965, 30585244671799959717, 336414893599428810601
OFFSET
0,2
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
Cf. A098158.
Sequence in context: A163308 A160112 A108427 * A142982 A218136 A196955
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