OFFSET
0,4
COMMENTS
Hankel transform is the (1,3) Somos-4 sequence A174170.
FORMULA
G.f.: (1-x+3x^2-sqrt(1-2x+3x^2-6x^3+9x^4))/(2x^2)=(1/(1+3x))*M(x/(1+3x^2)), M(x) the g.f. of A010006;
a(n) = sum{k=0..floor(n/2), (-3)^k*A001006(n-2k)}.
Conjecture: (n+2)*a(n) -(2*n+1)*a(n-1) +3*(n-1)*a(n-2) +3*(5-2*n)*a(n-3) +9*(n-4)*a(n-4)=0. - R. J. Mathar, Sep 30 2012
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Mar 10 2010
STATUS
approved