%I #26 Jun 29 2014 00:10:54
%S 1,2,72,115200,13276569600,165253252792320000,
%T 312379127174190543667200000,120053472861445542607502662277529600000,
%U 12098873398276702490569569159619238449643520000000000,400639807706466477973460949403651522366500906696560470917120000000000
%N 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)).
%C 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.
%H David M. Cerna, <a href="/A244148/b244148.txt">Table of n, a(n) for n = 1..50</a>
%H David M. Cerna, <a href="https://www.logic.at/sites/default/files/UP_0.pdf">Proof of enumeration formula </a>
%H Clark Kimberling, Unsolved Problems and Rewards: <a href="http://faculty.evansville.edu/ck6/integer/unsolved.html"> Number 18 </a>
%F a(n) = Prod_{k=1..n} (k!* binomial((n^2 - 3*n + 5*k - k^2)/2 , k)).
%o (PARI) a(n)=prod(k=1,n,k!* binomial((n^2 - 3*n + 5*k - k^2)/2 , k)); \\ _Joerg Arndt_, Jun 22 2014
%K easy,nonn
%O 1,2
%A _David M. Cerna_, Jun 21 2014