A026893 T(2n,n-3), T given by A026780.
1, 15, 144, 1137, 8070, 53678, 342224, 2119359, 12856752, 76826324, 453947206, 2659486160, 15479103062, 89636939038, 517014933254, 2972784038825, 17051188983758, 97611767361074, 557935896092592, 3185250335024206
Offset: 3