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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 123 |
| 5 | 786 |
| 6 | 6112 |
| 7 | 56504 |
| 8 | 607833 |
| 9 | 7467066 |
| 10 | 103120674 |
| 11 | 1580416008 |
| 12 | 26598861595 |
| 13 | 487397118314 |
| 14 | 9654657563748 |
| 15 | 205508121922824 |
| 16 | 4676833854264603 |
| 17 | 113293413849825702 |
| 18 | 2910255267932697130 |
| 19 | 79008535866112062440 |
| 20 | 2260164362082172615833 |
| 21 | 67947314033110789074486 |
[1,2,6,24,123,786,6112,56504,607833,7467066, 103120674,1580416008,26598861595,487397118314, 9654657563748,205508121922824,4676833854264603, 113293413849825702,2910255267932697130, 79008535866112062440,2260164362082172615833, 67947314033110789074486] |