A026651 a(n) = T(2n,n-2), T given by A026648.
1, 9, 40, 240, 915, 5103, 18704, 101952, 368490, 1990890, 7154928, 38514528, 138086403, 742202055, 2658662560, 14283407616, 51156225342, 274842096462, 984532674800, 5291030979360, 18960255044654, 101937273452454, 365451691152864
Offset: 2