OFFSET
1,9
COMMENTS
Row sums are A000110.
FORMULA
f(x, -1) = 1/(1 + x + x^2).
x + x^2*f(x, 2) = 1 - 1/f(x, 1) is g.f. for A074664.
EXAMPLE
Triangle starts:
1,
0, 1,
0, 1, 1,
0, 1, 3, 1,
0, 2, 6, 6, 1,
0, 5, 16, 20, 10, 1,
0, 15, 51, 71, 50, 15, 1,
0, 52, 186, 281, 231, 105, 21, 1,
0, 203, 759, 1223, 1114, 616, 196, 28, 1,
0, 877, 3409, 5795, 5701, 3564, 1428, 336, 36, 1,
...
MATHEMATICA
T[ n_, k_] := If[n < 0, 0, Coefficient[SeriesCoefficient[ Nest[ 1/(1 - x*y - x^2*y*(#/.y -> y+1))&, 1 + O[x], Ceiling[n/2]], {x, 0, n}], y, k]];
PROG
(PARI) {T(n, k) = if(n < 0, 0, f = 1 + O(x); forstep(i=1, n, 2, f = 1/(1 - x*y - x^2*y*subst(f, y, y+1))); polcoef(polcoef(f, n), k))};
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Michael Somos, Sep 27 2022
STATUS
approved