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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 110 |
| 5 | 544 |
| 6 | 5444 |
| 7 | 32520 |
| 8 | 385776 |
| 9 | 3282108 |
| 10 | 40916528 |
| 11 | 354328560 |
| 12 | 7200045216 |
| 13 | 67347823160 |
| 14 | 1182323197504 |
| 15 | 18086875471594 |
| 16 | 358787259407482 |
| 17 | 4564034487662420 |
[1,1,4,16,110,544,5444,32520,385776,3282108, 40916528,354328560,7200045216,67347823160, 1182323197504,18086875471594,358787259407482, 4564034487662420] |