| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 15 |
| 5 | 52 |
| 6 | 203 |
| 7 | 877 |
| 8 | 4140 |
| 9 | 21147 |
| 10 | 115975 |
| 11 | 678570 |
| 12 | 4213597 |
| 13 | 27644436 |
| 14 | 190899266 |
| 15 | 1382956734 |
| 16 | 10480097431 |
| 17 | 82863928963 |
| 18 | 682058946982 |
| 19 | 5832425824171 |
| 20 | 51718812364549 |
[1,1,2,5,15,52,203,877,4140,21147,115975,678570, 4213597,27644436,190899266,1382956734,10480097431, 82863928963,682058946982,5832425824171, 51718812364549] |