OFFSET
0,6
COMMENTS
Diagonal sums of number triangle A111963.
FORMULA
a(n)=sum{k=0..floor(n/2), sum{i=0..floor((n-k)/2), C(2i+2k-n-1, k)C(2i+k-n-1)(-1)^(n-k)*4^i}}
MATHEMATICA
CoefficientList[Series[1/(Sqrt[1+4x^2]+x(1-x)), {x, 0, 40}], x] (* Harvey P. Dale, May 27 2012 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Aug 23 2005
STATUS
approved