# A011958 (b-file synthesized from sequence entry) 1 1 2 1 3 3 4 8 5 22 6 68 7 216 8 728 9 2513 10 8920 11 32116 12 117240 13 431550 14 1600734 15 5970704 16 22381184 17 84236890 18 318191804 19 1205692236 20 4581481776 21 17452915218 22 66637798834 23 254960616136 24 977346581800 25 3753005281872