A026897 T(2n,n+4), T given by A026780.
1, 11, 80, 489, 2732, 14512, 74888, 380329, 1916709, 9637687, 48528434, 245289395, 1246499970, 6374296278, 32816505566, 170106486358, 887697088316, 4662338571684, 24636365887246, 130918389450108, 699335986465354
Offset: 4