The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 20 |
| 5 | 110 |
| 6 | 700 |
| 7 | 5005 |
| 8 | 40264 |
| 9 | 362796 |
| 10 | 3628680 |
| 11 | 39916635 |
| 12 | 479001380 |
| 13 | 6227020514 |
| 14 | 87178290836 |
| 15 | 1307674367545 |
| 16 | 20922789887440 |
| 17 | 355687428095320 |
| 18 | 6402373705727184 |
| 19 | 121645100408831031 |
| 20 | 2432902008176638860 |
| 21 | 51090942171709438670 |
| 22 | 1124000727777607678460 |
[1,1,2,5,20,110,700,5005,40264,362796,3628680, 39916635,479001380,6227020514,87178290836, 1307674367545,20922789887440,355687428095320, 6402373705727184,121645100408831031, 2432902008176638860,51090942171709438670, 1124000727777607678460] |