# A143648 (b-file synthesized from sequence entry) 0 1 1 4 2 22 3 136 4 868 5 5584 6 35992 7 232096 8 1496848 9 9653824 10 62262112 11 401558656 12 2589848128 13 16703198464 14 107727106432 15 694784866816 16 4481007870208 17 28900214293504 18 186391635645952 19 1202130942232576 20 7753131181401088