A026892 T(2n,n-4), T given by A026780.
1, 19, 220, 2021, 16246, 119914, 835080, 5579147, 36150820, 228879616, 1423367610, 8727874180, 52919787978, 317969615146, 1896431659490, 11241964305405, 66305996581006, 389432443869294, 2279159225280808
Offset: 4