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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 18 |
| 4 | 48 |
| 5 | 180 |
| 6 | 1080 |
| 7 | 7056 |
| 8 | 44928 |
| 9 | 286416 |
| 10 | 1762560 |
| 11 | 10349856 |
| 12 | 60217344 |
| 13 | 356638464 |
| 14 | 2145709440 |
| 15 | 12976433280 |
| 16 | 78399995904 |
| 17 | 472093588224 |
| 18 | 2832561529344 |
| 19 | 16960580969472 |
| 20 | 101554796888064 |
| 21 | 608733733690368 |
| 22 | 3652526115938304 |
| 23 | 21926115464435712 |
| 24 | 131620960833896448 |
[0,4,18,48,180,1080,7056,44928,286416,1762560, 10349856,60217344,356638464,2145709440, 12976433280,78399995904,472093588224, 2832561529344,16960580969472,101554796888064, 608733733690368,3652526115938304, 21926115464435712,131620960833896448] |