A244148 - OEIS

A244148

The number of ways one can assign values to n arrays a_{1},...,a_{n} of increasing size (size of a_{1} is 1, size of a_{2} is 2, ..., size of a_{n} is n) using the numbers 1, ..., n*(n+1)/2, distinctly, such that the positions of array a_{i} can only be assigned values in the interval ((n+1)-i),... , (n*(n+1)/2-(n-i)).

1, 2, 72, 115200, 13276569600, 165253252792320000, 312379127174190543667200000, 120053472861445542607502662277529600000, 12098873398276702490569569159619238449643520000000000, 400639807706466477973460949403651522366500906696560470917120000000000

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OFFSET

1,2

COMMENTS

This sequence provides an upper bound for the following sequence: the number of ways one can assign values to n arrays a_{1},...,a_{n} of increasing size (size of a_{1} is 1, size of a_{2} is 2, ..., size of a_{n} is n) using the numbers 1, ..., n*(n+1)/2, distinctly, such that for the j^th position of array a_{i} (a_{i}(j)) one of the follow holds, a_{i+1}(j+1) < a_{i}(j) < a_{i+1}(j) or a_{i+1}(j) < a_{i}(j) < a_{i+1}(j+1). Currently, there is no formula known for enumerating this sequence.

LINKS

David M. Cerna, Table of n, a(n) for n = 1..50

David M. Cerna, Proof of enumeration formula

Clark Kimberling, Unsolved Problems and Rewards: Number 18

FORMULA

a(n) = Prod_{k=1..n} (k!* binomial((n^2 - 3*n + 5*k - k^2)/2 , k)).

PROG

(PARI) a(n)=prod(k=1, n, k!* binomial((n^2 - 3*n + 5*k - k^2)/2 , k)); \\ Joerg Arndt, Jun 22 2014

CROSSREFS

Sequence in context: A062082 A067689 A308941 * A320443 A079478 A367492

Adjacent sequences: A244145 A244146 A244147 * A244149 A244150 A244151

KEYWORD

easy,nonn

AUTHOR

David M. Cerna, Jun 21 2014

STATUS

approved