OFFSET
1,3
COMMENTS
There are only m nonzero entries in the m-th column.
LINKS
G. C. Greubel, Rows n=1..30 of triangle, flattened
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (See the array on page 29.)
G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy)
EXAMPLE
Triangle begins:
1;
0, 2;
0, 3, 6;
0, 0, 20, 24;
0, 0, 15, 130, 120;
...
MATHEMATICA
T[n_, k_]:= If[k < 1 || k > n, 0, If[n==1 && k==1, 1, n*(T[n-1, k-1] + T[n-2, k-1])]]; Table[T[n, k], {n, 1, 10}, {k, 1, n}]//Flatten (* G. C. Greubel, Jan 17 2019 *)
PROG
(PARI) T(n, k)=if(k<=0 || k>n, 0, if(n==1 && k==1, 1, n*(T(n-1, k-1)+T(n-2, k-1))));
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
N. J. A. Sloane, Jan 21 2003
EXTENSIONS
Recurrence and more terms from Michael Somos, Jan 23 2003
Offset changed to 1 by G. C. Greubel, Jan 17 2019
STATUS
approved