A026093 T(2n,n+1), where T is the array defined in A026082.
1, 3, 27, 156, 925, 5427, 31812, 186485, 1094211, 6428346, 37817163, 222778629, 1314116799, 7761414055, 45894511305, 271681161390, 1609919112321, 9549113626206, 56690129330346, 336829717243428
Offset: 1