A156127 a(n) = 7*2^n - 3.

4, 11, 25, 53, 109, 221, 445, 893, 1789, 3581, 7165, 14333, 28669, 57341, 114685, 229373, 458749, 917501, 1835005, 3670013, 7340029, 14680061, 29360125, 58720253, 117440509, 234881021, 469762045, 939524093, 1879048189, 3758096381

Offset: 0

Author

Vincenzo Librandi, Feb 08 2009

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (3,-2).

Programs

Magma

I:=[4, 11]; [n le 2 select I[n] else 3*Self(n-1)-2*Self(n-2): n in [1..40]]; // Vincenzo Librandi, Mar 01 2012

Mathematica

LinearRecurrence[{3, -2}, {4, 11}, 40] (* Vincenzo Librandi, Mar 01 2012 *)

PARI

a(n)=7*2^n-3 \\ Charles R Greathouse IV, Oct 16 2015

Formula

a(n) = 2*a(n-1) + 3 with n > 0, a(0)=4.

G.f.: ( 4-x ) / ( (2*x-1)*(x-1) ). - R. J. Mathar, Oct 13 2011

Extensions

Corrected by R. J. Mathar, Oct 13 2011