The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 20 |
| 4 | 152 |
| 5 | 528 |
| 6 | 4416 |
| 7 | 15488 |
| 8 | 135552 |
| 9 | 477440 |
| 10 | 4289536 |
| 11 | 15144960 |
| 12 | 138407936 |
| 13 | 489431040 |
| 14 | 4526702592 |
| 15 | 16024403968 |
| 16 | 149528084480 |
| 17 | 529747476480 |
| 18 | 4977103994880 |
| 19 | 17643662213120 |
| 20 | 166668216041472 |
| 21 | 591119702294528 |
| 22 | 5608619676532736 |
[1,6,20,152,528,4416,15488,135552,477440,4289536, 15144960,138407936,489431040,4526702592, 16024403968,149528084480,529747476480, 4977103994880,17643662213120,166668216041472, 591119702294528,5608619676532736] |