| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 114 |
| 6 | 648 |
| 7 | 4284 |
| 8 | 32256 |
| 9 | 273616 |
| 10 | 2578352 |
| 11 | 26725776 |
| 12 | 302273664 |
| 13 | 3703441104 |
| 14 | 48865510848 |
| 15 | 690823736064 |
| 16 | 10417318281216 |
| 17 | 166907223390976 |
| 18 | 2831507368842752 |
| 19 | 50703852290781696 |
| 20 | 955742450175919104 |
| 21 | 18916030525704006144 |
| 22 | 392213482250102734848 |
[1,1,2,6,24,114,648,4284,32256,273616,2578352, 26725776,302273664,3703441104,48865510848, 690823736064,10417318281216,166907223390976, 2831507368842752,50703852290781696, 955742450175919104,18916030525704006144, 392213482250102734848] |