OFFSET
1,2
COMMENTS
Triangular array read by rows. For 0 <= k <= n-1, T(n,k) is the number of permutations of [n] for which the difference between the position of 1 and the position of the first weak subcedance is k. A weak subcedance of a permutation pi is an entry pi(i) such that pi(i) <= i. See link.
LINKS
FORMULA
T(1,0) = 1, T(n,0) = 2*(n-1)! + Sum_{j=1..n-2} j^(n-j-1)*j! for n >= 2, T(n,k) = (n-1)! - k^(n-k-1)*k! for 1 <= k <= n-1.
EXAMPLE
Triangle T(n,k) begins:
1;
2, 0;
5, 1, 0;
17, 5, 2, 0;
75, 23, 16, 6, 0;
407, 119, 104, 66, 24, 0;
2619, 719, 688, 558, 336, 120, 0;
19487, 5039, 4976, 4554, 3504, 2040, 720, 0;
164571, 40319, 40192, 38862, 34176, 25320, 14400, 5040, 0;
...
MATHEMATICA
a[1, 0] = 1;
a[n_, 0] /; n >= 2 := 2 (n - 1)! + Sum[k^(n - k - 1) k!, {k, 1, n - 2}];
a[n_, k_] /; n > k >= 1 := (n - 1)! - k^(n - k - 1) k!;
Flatten[Table[a[n, k], {n, 10}, {k, 0, n - 1}]]
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
David Callan, Dec 17 2021
STATUS
approved