The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 70 |
| 6 | 246 |
| 7 | 875 |
| 8 | 3144 |
| 9 | 11385 |
| 10 | 41470 |
| 11 | 151778 |
| 12 | 557712 |
| 13 | 2056210 |
| 14 | 7602700 |
| 15 | 28180050 |
| 16 | 104677280 |
| 17 | 389571983 |
| 18 | 1452293766 |
| 19 | 5422187130 |
| 20 | 20271296100 |
| 21 | 75878518695 |
| 22 | 284339792110 |
| 23 | 1066585128810 |
| 24 | 4004566131000 |
| 25 | 15048213795600 |
[1,2,6,20,70,246,875,3144,11385,41470,151778, 557712,2056210,7602700,28180050,104677280, 389571983,1452293766,5422187130,20271296100, 75878518695,284339792110,1066585128810, 4004566131000,15048213795600] |