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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 4 |
| 6 | 13 |
| 7 | 28 |
| 8 | 49 |
| 9 | 110 |
| 10 | 920 |
| 11 | 6322 |
| 12 | 30236 |
| 13 | 123737 |
| 14 | 790167 |
| 15 | 10430919 |
| 16 | 142197770 |
| 17 | 1546938330 |
| 18 | 16600218633 |
| 19 | 257429254996 |
| 20 | 6152180165653 |
[1,4,13,28,49,110,920,6322,30236,123737,790167, 10430919,142197770,1546938330,16600218633, 257429254996,6152180165653] |