A047123 T(n,n-1), array T as in A047120.
1, 1, 4, 16, 58, 215, 806, 3051, 11602, 44307, 169840, 653204, 2519314, 9740350, 37739300, 146498531, 569642584, 2218322463, 8650367796, 33773500347, 132008143328, 516495270723, 2022721237326, 7928249018667, 31100068617294
Offset: 1