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A198647
3*7^n-1
8
2, 20, 146, 1028, 7202, 50420, 352946, 2470628, 17294402, 121060820, 847425746, 5931980228, 41523861602, 290667031220, 2034669218546, 14242684529828, 99698791708802, 697891541961620, 4885240793731346, 34196685556119428
OFFSET
0,1
FORMULA
a(n) = 7*a(n-1)+6, a(0)=2.
G.f.: ( 2+4*x ) / ( (7*x-1)*(x-1) ). - R. J. Mathar, Oct 30 2011
a(n) = 8*a(n-1) - 7*a(n-2). - Harvey P. Dale, Jan 27 2012
MATHEMATICA
3*7^Range[0, 20]-1 (* or *) LinearRecurrence[{8, -7}, {2, 20}, 20] (* Harvey P. Dale, Jan 27 2012 *)
PROG
(Magma) [3*7^n-1: n in [0..30]]
(PARI) a(n)=3*7^n-1 \\ Charles R Greathouse IV, Nov 21 2011
CROSSREFS
Sequence in context: A000183 A198052 A203216 * A081159 A105489 A093302
KEYWORD
nonn,easy,less
AUTHOR
Vincenzo Librandi, Oct 28 2011
STATUS
approved