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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 10 |
| 3 | 40 |
| 4 | 215 |
| 5 | 1260 |
| 6 | 8010 |
| 7 | 53240 |
| 8 | 366680 |
| 9 | 2590420 |
| 10 | 18674660 |
| 11 | 136809240 |
| 12 | 1015603015 |
| 13 | 7622900360 |
| 14 | 57753364510 |
| 15 | 441081947840 |
| 16 | 3392237023425 |
| 17 | 26248421645200 |
| 18 | 204202630151860 |
| 19 | 1596256637347240 |
| 20 | 12531697773337965 |
| 21 | 98763817012822460 |
| 22 | 781102051887068160 |
[4,10,40,215,1260,8010,53240,366680,2590420, 18674660,136809240,1015603015,7622900360, 57753364510,441081947840,3392237023425, 26248421645200,204202630151860,1596256637347240, 12531697773337965,98763817012822460, 781102051887068160] |