The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 60 |
| 5 | 500 |
| 6 | 5160 |
| 7 | 64050 |
| 8 | 925680 |
| 9 | 15274224 |
| 10 | 283681440 |
| 11 | 5858178480 |
| 12 | 133168432320 |
| 13 | 3305096308800 |
| 14 | 88940036465280 |
| 15 | 2579622274429200 |
| 16 | 80228312766201600 |
| 17 | 2663566170795129600 |
| 18 | 94025979044975577600 |
| 19 | 3516890931415484663040 |
| 20 | 138943364103192391142400 |
[1,1,2,9,60,500,5160,64050,925680,15274224, 283681440,5858178480,133168432320,3305096308800, 88940036465280,2579622274429200,80228312766201600, 2663566170795129600,94025979044975577600, 3516890931415484663040,138943364103192391142400] |