OFFSET
0,2
FORMULA
a(n)=sum{k=0..n, sum{j=0..k, C(k,j)*C(k-j,j)*(-1)^j}}
D-finite with recurrence: n*a(n) +(-3*n+1)*a(n-1) +(7*n-6)*a(n-2) +5*(-n+1)*a(n-3)=0. - R. J. Mathar, Jan 23 2020
MATHEMATICA
CoefficientList[Series[1/((1-x)Sqrt[1-2x+5x^2]), {x, 0, 50}], x] (* Harvey P. Dale, Jun 23 2018 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Feb 13 2007
STATUS
approved