OFFSET
0,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
G.f.: x*(3*x+12*x^2+1)/(x-1)^2.
a(n) = 2*a(n-1) -a(n-2), n>=4.
a(n) = 4*A016813(n-2) + 1, n>=2. - Ivan N. Ianakiev, Jul 20 2013
MATHEMATICA
CoefficientList[Series[x*(3*x + 12*x^2 + 1)/(x - 1)^2, {x, 0, 60}], x] (* Vincenzo Librandi, Dec 19 2012 *)
LinearRecurrence[{2, -1}, {0, 1, 5, 21}, 60] (* Harvey P. Dale, Oct 09 2017 *)
PROG
(Magma) I:=[0, 1, 5, 21]; [n le 4 select I[n] else 2*Self(n-1) - Self(n-2): n in [1..60]]; // Vincenzo Librandi, Dec 19 2012
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jan 05 2010, based on email from R. J. Mathar and Benoit Jubin, Jun 02 2009; revised Jan 09 2010
STATUS
approved