The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 20 |
| 4 | 94 |
| 5 | 507 |
| 6 | 3009 |
| 7 | 19350 |
| 8 | 132920 |
| 9 | 966962 |
| 10 | 7396366 |
| 11 | 59173897 |
| 12 | 492995320 |
| 13 | 4262193275 |
| 14 | 38125138575 |
| 15 | 351960913470 |
| 16 | 3346157796060 |
| 17 | 32700768584100 |
| 18 | 327957494280000 |
| 19 | 3370522049859990 |
| 20 | 35451669429671520 |
| 21 | 381183654441916290 |
[1,2,5,20,94,507,3009,19350,132920,966962,7396366, 59173897,492995320,4262193275,38125138575, 351960913470,3346157796060,32700768584100, 327957494280000,3370522049859990, 35451669429671520,381183654441916290] |