OFFSET
0,2
COMMENTS
a(0)=1, a(2n-1)=k^(2n-1), a(2n)=(2-k)k^(2n-1), k=5; G.f.: (1+kx+(2-2k)kx^2)/((1-kx)(1+kx)), k=5.
LINKS
FORMULA
a(n)=5^n/5 +(-4)(-5)^n/5+8*0^n/5
MATHEMATICA
CoefficientList[Series[(1+5x-40x^2)/((1-5x)(1+5x)), {x, 0, 30}], x] (* or *) LinearRecurrence[{0, 25}, {1, 5, -15}, 30] (* Harvey P. Dale, Dec 26 2015 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Dec 19 2003
STATUS
approved