OFFSET
0,2
COMMENTS
Diagonal sums of number triangle A106190.
FORMULA
a(n) = Sum_{k=0..floor(n/2)} binomial(2*(n-2*k), n-2*k)/(1-2*(n-2*k)).
D-finite with recurrence: n*a(n) +2*(-2*n+3)*a(n-1) -n*a(n-2) +2*(2*n-3)*a(n-3)=0. - R. J. Mathar, Nov 28 2014
MATHEMATICA
CoefficientList[Series[Sqrt[1-4x]/(1-x^2), {x, 0, 30}], x] (* Harvey P. Dale, Apr 24 2012 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Apr 24 2005
STATUS
approved