OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Index entries for linear recurrences with constant coefficients, signature (39,-351,729).
FORMULA
G.f.: 1/((1-3*x)*(1-9*x)*(1-27*x)).
a(n) = 3^n*(3^(n+1)-1)*(3^(n+2)-1)/16.
a(0)=1, a(1)=39, a(2)=1170; for n>2, a(n) = 39*a(n-1)-351*a(n-2)+729*a(n-3).
a(n)-27*a(n-1) = A016142(n), with a(-1)=0; a(n) = A226804(n)-81*A226804(n-1), with A226804(-1)=0. [Bruno Berselli, Jul 17 2013]
MATHEMATICA
CoefficientList[Series[1 / ((1 - 3 x) (1 - 9 x) (1 - 27 x)), {x, 0, 30}], x]
LinearRecurrence[{39, -351, 729}, {1, 39, 1170}, 20] (* Harvey P. Dale, Jul 04 2022 *)
PROG
(Magma) m:=25; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/((1-3*x)*(1-9*x)*(1-27*x)))); /* or */ I:=[1, 39, 1170]; [n le 3 select I[n] else 39*Self(n-1)-351*Self(n-2)+729*Self(n-3): n in [1..25]];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Jul 17 2013
STATUS
approved