OFFSET
0,5
COMMENTS
FORMULA
G.f.: (1+x+x^2+x^3)(1+xy+x^2*y^2+x^3*y^3)/((1-x^4)^2*(1-x^4*y^4)^2*(1-x^2*y)); Number triangle T(n, k)=sum{j=0..n, [j<=k]*floor((k-j+4)/4)*[j<=n-k]*floor((n-k-j+4)/4)}.
EXAMPLE
Triangle begins
1;
1,1;
1,2,1;
1,2,2,1;
2,2,3,2,2;
2,3,3,3,3,2;
2,4,4,4,4,4,2;
2,4,5,5,5,5,4,2;
3,4,6,6,8,6,6,4,3;
3,5,6,7,9,9,7,6,5,3;
3,6,7,8,10,12,10,8,7,6,3;
3,6,8,9,11,13,13,11,9,8,6,3;
CROSSREFS
KEYWORD
AUTHOR
Paul Barry, Jan 18 2006
STATUS
approved