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A221904
a(n) = 9^n + 10^n.
1
2, 19, 181, 1729, 16561, 159049, 1531441, 14782969, 143046721, 1387420489, 13486784401, 131381059609, 1282429536481, 12541865828329, 122876792454961, 1205891132094649, 11853020188851841
OFFSET
0,1
FORMULA
G.f.: 1/(1 - 9*x) + 1/(1 - 10*x).
E.g.f.: exp(9*x) + exp(10*x).
a(n) = 19*a(n-1) - 90*a(n-2), a(1)=2, a(2)=19.
MATHEMATICA
CoefficientList[Series[1/(1-9*x) + 1/(1-10*x), {x, 0, 30}], x]
LinearRecurrence[{19, -90}, {2, 19}, 30] (* Harvey P. Dale, Nov 10 2017 *)
PROG
(Magma) [9^n + 10^n: n in [0..30]];
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Feb 06 2013
STATUS
approved