OFFSET
0,2
LINKS
FORMULA
a(n) = 2*3^n/3 + 5*(-3)^n/3 - 4*0^n/3.
a(0)=1, a(2n-1)=-k^(2n-1), a(2n)=(3k-2)*k^(2n-1), where k=3.
G.f.: (1-k*x+2*(k-1)*k*x^2)/((1-k*x)*(1+k*x)), where k=3.
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Dec 22 2003
STATUS
approved