# A037788 (b-file synthesized from sequence entry) 1 3 2 20 3 120 4 721 5 4329 6 25976 7 155856 8 935137 9 5610825 10 33664952 11 201989712 12 1211938273 13 7271629641 14 43629777848 15 261778667088 16 1570672002529 17 9424032015177 18 56544192091064 19 339265152546384 20 2035590915278305