OFFSET
1,1
COMMENTS
All entries are multiples of 3.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (-1,-3,-3)
FORMULA
a(2n)+a(2n+1) = (-1)^n*A000244(n).
a(n) = (3/2) * ((2*(-1)^n - 3) * (-3)^floor(n/2) - 3*(-1)^n ). - Ralf Stephan, Aug 17 2013
MATHEMATICA
CoefficientList[Series[3 (3 x + 1) (2 x - 1) / ((1 + x) (3 x^2 + 1)), {x, 0, 40}], x] (* Vincenzo Librandi, Aug 17 2013 *)
LinearRecurrence[{-1, -3, -3}, {-3, 0, 27}, 40] (* Harvey P. Dale, Dec 26 2014 *)
PROG
(PARI) a(n)=3/2*((2*(-1)^n-3)*(-3)^floor(n/2)-3*(-1)^n); \\ Ralf Stephan, Aug 17 2013
(Magma) I:=[-3, 0, 27]; [n le 3 select I[n] else -Self(n-1)-3*Self(n-2) -3*Self(n-3): n in [1..50]]; // Vincenzo Librandi, Aug 17 2013
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Paul Curtz, Aug 31 2008
STATUS
approved