A381759 Number of words of length 2n+1 with one 0 entry and two entries of each of 1..n so that there are exactly k numbers between two equal k's and so that the first element does not exceed the last.
1, 1, 3, 5, 11, 38, 182, 938, 4158, 23384, 160104, 1063772, 6987380, 53746000, 479965824, 4182552416, 35963592624, 351432650816, 3860219984448, 41614300175968
Offset: 1
Examples
a(4) = 5 since there are 5 different solutions: 131423024, 141302432, 240231413, 023421314, 041312432.