# A019309 (b-file synthesized from sequence entry)
0 1
1 4
2 12
3 48
4 180
5 720
6 2832
7 11328
8 45132
9 180528
10 721392
11 2885568
12 11539440
13 46157760
14 184619712
15 738478848
16 2953870260
17 11815481040
18 47261743632
19 189046974528
20 756187176720
21 3024748706880
22 12098991941952