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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 9 |
| 4 | 18 |
| 5 | 33 |
| 6 | 60 |
| 7 | 105 |
| 8 | 180 |
| 9 | 309 |
| 10 | 526 |
| 11 | 895 |
| 12 | 1520 |
| 13 | 2581 |
| 14 | 4378 |
| 15 | 7427 |
| 16 | 12596 |
[1,4,9,18,33,60,105,180,309,526,895,1520,2581, 4378,7427,12596] |