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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 120 |
| 4 | 612 |
| 5 | 2532 |
| 6 | 10800 |
| 7 | 45380 |
| 8 | 182768 |
| 9 | 728848 |
| 10 | 2917132 |
| 11 | 11771140 |
| 12 | 47229148 |
| 13 | 188138496 |
| 14 | 753562420 |
| 15 | 3021549192 |
[1,4,24,120,612,2532,10800,45380,182768,728848, 2917132,11771140,47229148,188138496,753562420, 3021549192] |