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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 9 |
| 5 | 45 |
| 6 | 76 |
| 7 | 270 |
| 8 | 2204 |
| 9 | 3718 |
| 10 | 95499 |
| 11 | 590890 |
| 12 | 16023339 |
| 13 | 16475964 |
| 14 | 1745175039 |
| 15 | 31287652672 |
| 16 | 347321438520 |
| 17 | 2620400333120 |
| 18 | 239919791836864 |
[1,1,4,9,45,76,270,2204,3718,95499,590890, 16023339,16475964,1745175039,31287652672, 347321438520,2620400333120,239919791836864] |