# A006725 (b-file synthesized from sequence entry) 1 1 2 2 3 6 4 18 5 55 6 174 7 566 8 1868 9 6237 10 21050 11 71666 12 245696 13 847317 14 2937116 15 10226574 16 35746292 17 125380257 18 441125966 19 1556301578 20 18155586993