A026896 T(2n,n+3), T given by A026780.
1, 9, 57, 316, 1647, 8330, 41558, 206418, 1026392, 5126109, 25763881, 130446758, 665644541, 3423360416, 17740450004, 92599616864, 486607242642, 2573051443194, 13683364565774, 73146530405912, 392867752273562, 2119154966713452
Offset: 3