A131131 4*A007318 - 3*A097806.
1, 1, 1, 4, 5, 1, 4, 12, 9, 1, 4, 16, 24, 13, 1, 4, 20, 40, 40, 17, 1, 4, 24, 60, 80, 60, 21, 1, 4, 28, 84, 140, 140, 84, 25, 1, 4, 32, 112, 224, 280, 224, 112, 29, 1
Offset: 0
Examples
First few rows of the triangle: 1; 1, 1; 4, 5, 1; 4, 12, 9, 1; 4, 16, 24, 13, 1 4, 20, 40, 40, 17, 1; ...
Formula
G.f.: (1-x*y+3*x^2+3*x^2*y)/((-1+x+x*y)*(x*y-1)). - R. J. Mathar, Aug 12 2015
Comments