A026859 T(2n,n-4), T given by A026747.
1, 15, 141, 1070, 7187, 44673, 263431, 1496218, 8266100, 44718596, 238015318, 1250656153, 6504202391, 33543967700, 171810543570, 875006817465, 4435130657170, 22390449598704, 112654298838120, 565172299571352
Offset: 4