OFFSET
0,3
FORMULA
a(n)=(-1)^C(n,2)*(C(n,n/2)*(1+(-1)^n)/2+C(n-1,(n-1)/2)*(1-(-1)^n)/2);
Conjecture: n*(5*n-9)*a(n) +4*a(n-1) +4*(5*n-4)*(n-2)*a(n-2)=0. - R. J. Mathar, Dec 02 2014
D-finite with recurrence: n*a(n) +(n-2)*a(n-1) +4*(n-1)*a(n-2) +4*(n-3)*a(n-3)=0. - R. J. Mathar, Dec 02 2014
MATHEMATICA
CoefficientList[Series[(1+x)/Sqrt[1+4x^2], {x, 0, 40}], x] (* Harvey P. Dale, May 12 2015 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Feb 13 2007
STATUS
approved