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A133647
2
1, 3, 12, 27, 108, 243, 972, 2187, 8748, 19683, 78732, 177147, 708588, 1594323, 6377292, 14348907, 57395628, 129140163, 516560652, 1162261467, 4649045868, 10460353203, 41841412812, 94143178827, 376572715308
OFFSET
0,2
COMMENTS
A133646 is a companion case.
FORMULA
A133566 * A000244, where A133566 = an infinite lower triangular matrix and A000244 = [3^0, 3^1, 3^2, ...]. For odd n, a(n) = 3^n. For even n, a(n) = 4 * 3^(n-1).
G.f.: (1+3*x+3*x^2)/(1-9*x^2). - Philippe Deléham, Apr 06 2012
a(n+2) = 9*a(n), a(0) = 1, a(1) = 3, a(2) = 12. - Philippe Deléham, Apr 06 2012
EXAMPLE
a(3) = 27 = 3^3.
a(4) = 108 = 4 * 3^3.
MATHEMATICA
Join[{1}, Flatten[NestList[9#&, {3, 12}, 20]]] (* or *) LinearRecurrence[{0, 9}, {1, 3, 12}, 40] (* Harvey P. Dale, Aug 01 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Gary W. Adamson, Sep 19 2007
EXTENSIONS
More terms from Philippe Deléham, Apr 06 2012
STATUS
approved