OFFSET
1,2
LINKS
FORMULA
G.f.: x*(1+3*x) / ( (x-1)*(9*x-1)*(1+x+x^2) ). - R. J. Mathar, Apr 27 2015
PROG
(PARI) a(n)=([0, 1, 0, 0; 0, 0, 1, 0; 0, 0, 0, 1; -9, 1, 0, 9]^(n-1)*[1; 12; 108; 973])[1, 1] \\ Charles R Greathouse IV, Feb 13 2017
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
STATUS
approved