# A019308 (b-file synthesized from sequence entry) 0 1 1 3 2 6 3 18 4 48 5 144 6 414 7 1242 8 3678 9 11034 10 32958 11 98874 12 296208 13 888624 14 2664630 15 7993890 16 23977992 17 71933976 18 215790894 19 647372682 20 1942085088 21 5826255264 22 17478666918 23 52436000754 24 157307706054 25 471923118162