The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 13 |
| 3 | 72 |
| 4 | 417 |
| 5 | 2509 |
| 6 | 15438 |
| 7 | 96310 |
| 8 | 607231 |
| 9 | 3859594 |
| 10 | 24689329 |
| 11 | 158756701 |
| 12 | 1025210362 |
| 13 | 6644336882 |
| 14 | 43193144567 |
| 15 | 281525730152 |
| 16 | 1839132807282 |
| 17 | 12038672624172 |
| 18 | 78943126865652 |
| 19 | 518485130526736 |
| 20 | 3410150902046028 |
[1,3,13,72,417,2509,15438,96310,607231,3859594, 24689329,158756701,1025210362,6644336882, 43193144567,281525730152,1839132807282, 12038672624172,78943126865652,518485130526736, 3410150902046028] |