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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 521 |
| 3 | 17136 |
| 4 | 320716 |
| 5 | 4356560 |
| 6 | 48024786 |
| 7 | 456843520 |
| 8 | 3893995184 |
| 9 | 30487086144 |
| 10 | 223052123830 |
| 11 | 1544098243424 |
| 12 | 10208488021176 |
| 13 | 64917814932256 |
| 14 | 399310478637476 |
| 15 | 2386386863086080 |
| 16 | 13906802738650816 |
| 17 | 79261768839946496 |
| 18 | 442921922267640894 |
[0,4,521,17136,320716,4356560,48024786,456843520, 3893995184,30487086144,223052123830,1544098243424, 10208488021176,64917814932256,399310478637476, 2386386863086080,13906802738650816, 79261768839946496,442921922267640894] |