| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 104 |
| 6 | 464 |
| 7 | 2088 |
| 8 | 9392 |
| 9 | 42064 |
| 10 | 187296 |
| 11 | 828776 |
| 12 | 3644912 |
| 13 | 15937776 |
| 14 | 69317984 |
| 15 | 300009744 |
| 16 | 1292654304 |
| 17 | 5547021728 |
| 18 | 23715100480 |
| 19 | 101046014952 |
| 20 | 429209373296 |
| 21 | 1817975905456 |
| 22 | 7680278380512 |
| 23 | 32368750662320 |
[1,2,6,24,104,464,2088,9392,42064,187296,828776, 3644912,15937776,69317984,300009744,1292654304, 5547021728,23715100480,101046014952,429209373296, 1817975905456,7680278380512,32368750662320] |