The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 67 |
| 6 | 238 |
| 7 | 889 |
| 8 | 3430 |
| 9 | 13502 |
| 10 | 54133 |
| 11 | 220602 |
| 12 | 912169 |
| 13 | 3814549 |
| 14 | 16105873 |
| 15 | 68586793 |
| 16 | 294388261 |
| 17 | 1272134186 |
| 18 | 5530081563 |
| 19 | 24168691099 |
| 20 | 106150861556 |
| 21 | 468293726986 |
| 22 | 2074232732996 |
| 23 | 9221208846420 |
| 24 | 41133693548902 |
| 25 | 184061536758043 |
| 26 | 825997748283384 |
| 27 | 3716645799512423 |
| 28 | 16765083601178960 |
[1,1,2,6,20,67,238,889,3430,13502,54133,220602, 912169,3814549,16105873,68586793,294388261, 1272134186,5530081563,24168691099,106150861556, 468293726986,2074232732996,9221208846420, 41133693548902,184061536758043,825997748283384, 3716645799512423,16765083601178960] |