A198647 3*7^n-1.

2, 20, 146, 1028, 7202, 50420, 352946, 2470628, 17294402, 121060820, 847425746, 5931980228, 41523861602, 290667031220, 2034669218546, 14242684529828, 99698791708802, 697891541961620, 4885240793731346, 34196685556119428

Offset: 0

Author

Vincenzo Librandi, Oct 28 2011

Keywords

• nonn
• easy
• less

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (8,-7).

Programs

Magma

[3*7^n-1: n in [0..30]]

Mathematica

3*7^Range[0,20]-1 (* or *) LinearRecurrence[{8,-7},{2,20},20] (* Harvey P. Dale, Jan 27 2012 *)

PARI

a(n)=3*7^n-1 \\ Charles R Greathouse IV, Nov 21 2011

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