OFFSET
1,3
COMMENTS
Except for the number 2, it contains all the positive integers.
FORMULA
T(n, k) = 1 + Sum_{i=1..k-1} (n - i + 1).
From R. J. Mathar, Feb 07 2022: (Start)
G.f.: x*y*(1 - x + y*x^2 + y^2*x^3)/((1 - x)^2*(1 - y*x)^3).
EXAMPLE
Triangle begins:
1;
1, 3;
1, 4, 6;
1, 5, 8, 10;
1, 6, 10, 13, 15;
1, 7, 12, 16, 19, 21;
1, 8, 14, 19, 23, 26, 28;
...
MATHEMATICA
Flatten[Table[n(k-1)-k(k-3)/2, {n, 12}, {k, n}]]
CROSSREFS
KEYWORD
AUTHOR
Stefano Spezia, Feb 02 2022
STATUS
approved