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A198686
4*7^n-1.
1
3, 27, 195, 1371, 9603, 67227, 470595, 3294171, 23059203, 161414427, 1129900995, 7909306971, 55365148803, 387556041627, 2712892291395, 18990246039771, 132931722278403, 930522055948827, 6513654391641795, 45595580741492571
OFFSET
0,1
FORMULA
a(n) = 7*a(n-1)+6. a(n) = 8*a(n-1)-7*a(n-2), n>1.
G.f. ( 3+3*x ) / ( (7*x-1)*(x-1) ). - R. J. Mathar, Oct 30 2011
MATHEMATICA
4*7^Range[0, 20]-1 (* or *) LinearRecurrence[{8, -7}, {3, 27}, 20] (* Harvey P. Dale, Dec 27 2011 *)
PROG
(Magma) [4*7^n-1: n in [0..30]]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Oct 29 2011
STATUS
approved