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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 30 |
| 4 | 154 |
| 5 | 1105 |
| 6 | 4788 |
| 7 | 20677 |
| 8 | 216931 |
| 9 | 858925 |
| 10 | 7105392 |
| 11 | 5546059 |
| 12 | 2018025900 |
| 13 | 1480452337 |
| 14 | 3238556831 |
| 15 | 107972737 |
| 16 | 18425956230000 |
| 17 | 4683032671 |
| 18 | 14053747110612300 |
| 19 | 160436746661 |
| 20 | 33809725025123 |
| 21 | 15260431896321667 |
| 22 | 1583855315457687090000 |
[1,2,6,30,154,1105,4788,20677,216931,858925, 7105392,5546059,2018025900,1480452337,3238556831, 107972737,18425956230000,4683032671, 14053747110612300,160436746661,33809725025123, 15260431896321667,1583855315457687090000] |