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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 24 |
| 3 | 168 |
| 4 | 972 |
| 5 | 5200 |
| 6 | 26632 |
| 7 | 134898 |
| 8 | 668668 |
| 9 | 3278294 |
| 10 | 15902088 |
| 11 | 76515244 |
| 12 | 365585432 |
| 13 | 1736575416 |
| 14 | 8206953072 |
| 15 | 38615236370 |
| 16 | 180986296644 |
| 17 | 845359203352 |
| 18 | 3936439186972 |
| 19 | 18279759467004 |
| 20 | 84675466304900 |
| 21 | 391350188916098 |
[2,24,168,972,5200,26632,134898,668668,3278294, 15902088,76515244,365585432,1736575416,8206953072, 38615236370,180986296644,845359203352, 3936439186972,18279759467004,84675466304900, 391350188916098] |