cp's OEIS Frontend

A221624 Number of 2Xn arrays with each row a permutation of 1..n having at least as many downsteps as the preceding row.

%I A221624 #6 Jul 23 2025 02:03:53
%S A221624 1,3,27,410,10055,353654,17052210,1075295220,86037489675,
%T A221624 8510611773950,1020010974544958,145633667181394028,
%U A221624 24424236713657975558,4754016566455947216412,1062903928921857001102308
%N A221624 Number of 2Xn arrays with each row a permutation of 1..n having at least as many downsteps as the preceding row.
%C A221624 Row 2 of A221623
%H A221624 R. H. Hardin, <a href="/A221624/b221624.txt">Table of n, a(n) for n = 1..16</a>
%e A221624 Some solutions for n=3
%e A221624 ..2..3..1....2..3..1....2..1..3....3..1..2....2..1..3....1..3..2....1..2..3
%e A221624 ..3..2..1....1..3..2....2..3..1....2..1..3....2..1..3....2..3..1....1..2..3
%K A221624 nonn
%O A221624 1,2
%A A221624 _R. H. Hardin_ Jan 21 2013