The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 118 |
| 6 | 675 |
| 7 | 4333 |
| 8 | 30464 |
| 9 | 230615 |
| 10 | 1856336 |
| 11 | 15738672 |
| 12 | 139509303 |
| 13 | 1285276242 |
| 14 | 12248071935 |
| 15 | 120255584181 |
| 16 | 1212503440774 |
| 17 | 12519867688928 |
| 18 | 132079067871313 |
| 19 | 1420723274988736 |
| 20 | 15554956521285848 |
[1,2,6,24,118,675,4333,30464,230615,1856336, 15738672,139509303,1285276242,12248071935, 120255584181,1212503440774,12519867688928, 132079067871313,1420723274988736, 15554956521285848] |