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URL: https://oeis.org/A090441

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A090441
Symmetric triangle of certain normalized products of decreasing factorials.
6
1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 6, 12, 6, 1, 1, 24, 144, 144, 24, 1, 1, 120, 2880, 8640, 2880, 120, 1, 1, 720, 86400, 1036800, 1036800, 86400, 720, 1, 1, 5040, 3628800, 217728000, 870912000, 217728000, 3628800, 5040, 1, 1, 40320, 203212800, 73156608000
OFFSET
0,8
COMMENTS
Similar to, but different from, superfactorial Pascal triangle A009963.
A009963(n,m) = (Product_{p=0..m-1} (n-p)!)/superfac(m) with n >= m >= 0, otherwise 0.
From Natalia L. Skirrow, Apr 13 2025 (Start)
Denoting this sequence as the superbinomial sb(n,k), the hook length formula for a j X k rectangular Young tableau states the number of configurations of j*k distinct numbers such that each row and column is strictly increasing is (j*k)!/sb(j+k,j), ie. 1/sb(j+k,j) is the probability that a random permutation is a Young tableau.
Meanwhile, if the numbers are placed into the array with repetition, but the columns are still strictly increasing, there are c(n,j,k) = sb(n+1,j+k)/(sb(n+1-j,k)*sb(n+1-k,j)) configurations.
If the strict criterion is relaxed to monotonic, this becomes C(n,j,k) = sb(n-1+j+k,j+k)/(sb(n-1+j,j)*sb(n-1+k,k)).
By proposition 13.2(i) of Stanley's PhD thesis, for fixed j,k, c(n,j,k) and C(n,j,k) are polynomials in n of degree j*k, and c(n,j,k) = (-1)^(j*k)*C(-n,j,k).
For example, c(n,1,k)=(n choose k) and C(n,1,k)=(n+k-1 choose k), while c(n,2,k) = N(n,k+1) and C(n,2,k) = N(n+k,k+1), so the binomial coefficients and Narayana numbers N=A001263 obey the dualities (under continuation as polynomials) (n choose k) = (-1)^k*(k-1-n choose k) and N(n,k) = N(k-1-n,k).
(End)
LINKS
Donald Knuth, Two Notes on Notation, arXiv:math/9205211 [math.HO], 1992. (Page 16-17 explain and give examples; the case with Narayana numbers come from tying together the poset P_k's 'shoelaces' with inequalities, into a 2 X k rectangle.)
Wolfdieter Lang, First 9 rows
Richard P. Stanley, Ordered Structures and Partitions, 1971.
FORMULA
a(n, m) = 0 if n < m;
a(n, m) = 1 if m = 0 or m = n;
a(n, m) = (Product_{p=1..m} (n-p)!)/superfac(m-1) if n >= 0, 1 <= m <= n+1, where superfac(n) := A000178(n), n >= 0, (superfactorials).
a(n, m) = superfac(n-1)/superfac(m-1)/superfac(n-m-1)
With offset 1, equals ConvOffsStoT transform of the factorials, A000142: (1, 1, 2, 6, 24, ...); e.g., ConvOffs transform of (1, 1, 2, 6) = (1, 6, 12, 6, 1). - Gary W. Adamson, Apr 21 2008
EXAMPLE
Rows for n = 0, 1, 2, 3, ...:
1;
1, 1;
1, 1, 1;
1, 2, 2, 1;
1, 6, 12, 6, 1;
...
PROG
(PARI) spf(n) = prod(k=2, n, k!);
T(n, m) = spf(n-1)/spf(m-1)/spf(n-m-1);
row(n) = vector(n+1, k, T(n, k-1)); \\ Michel Marcus, Apr 13 2025
CROSSREFS
Column sequences give: A000012 (powers of 1), A000142 (factorials), A010790, A090443-4, etc.
Cf. A090445 (row sums), A090446 (alternating row sums).
Sequence in context: A138169 A139331 A173886 * A340591 A155794 A381854
KEYWORD
nonn,easy,tabl
AUTHOR
Wolfdieter Lang, Dec 23 2003
EXTENSIONS
OFFSET changed from -1 to 0 by Natalia L. Skirrow, Apr 13 2025
STATUS
approved