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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 12 |
| 3 | 36 |
| 4 | 108 |
| 5 | 264 |
| 6 | 708 |
| 7 | 1668 |
| 8 | 4536 |
| 9 | 10926 |
| 10 | 28416 |
| 11 | 67824 |
| 12 | 172464 |
| 13 | 408484 |
| 14 | 1035932 |
[1,4,12,36,108,264,708,1668,4536,10926,28416, 67824,172464,408484,1035932] |