OFFSET
0,4
COMMENTS
Diagonal sums of Riordan array (1,x(1-3x)).
LINKS
FORMULA
G.f.: 1/(1-x^2+3x^3); a(n)=a(n-2)-3a(n-3); a(n)=sum{k=0..floor(n/2), (-1)^n*binomial(k, n-2k)*3^(n-2k)}.
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, May 08 2005
STATUS
approved