OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (21,-128,240).
FORMULA
a(n) = 2*4^n - 25*5^n/7 + 18*12^n/7. - R. J. Mathar, Jun 29 2013
From Vincenzo Librandi, Jul 02 2013: (Start)
a(n) = 21*a(n-1) - 128*a(n-2) + 240*a(n-3) for n > 2; a(0)=1, a(1)=21, a(2)=313.
a(n) = 17*a(n-1) - 60*a(n-2) + 4^n. (End)
MATHEMATICA
CoefficientList[Series[1 / ((1 - 4 x) (1 - 5 x) (1 - 12 x)), {x, 0, 20}], x] (* Vincenzo Librandi, Jul 02 2013 *)
LinearRecurrence[{21, -128, 240}, {1, 21, 313}, 20] (* Harvey P. Dale, Mar 09 2022 *)
PROG
(Magma) m:=20; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/((1-4*x)*(1-5*x)*(1-12*x)))); /* or */ I:=[1, 21, 313]; [n le 3 select I[n] else 21*Self(n-1)-128*Self(n-2)+240*Self(n-3): n in [1..20]]; // Vincenzo Librandi, Jul 02 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved