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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 30 |
| 4 | 324 |
| 5 | 4540 |
| 6 | 78060 |
| 7 | 1589448 |
| 8 | 37388400 |
| 9 | 997513200 |
| 10 | 29759790240 |
| 11 | 981669324240 |
| 12 | 35475203063520 |
| 13 | 1393746645107232 |
| 14 | 59147129937893088 |
| 15 | 2696314664384853120 |
| 16 | 131405475202661963520 |
| 17 | 6817779852438948837120 |
| 18 | 375193156508083422581760 |
[1,1,4,30,324,4540,78060,1589448,37388400, 997513200,29759790240,981669324240,35475203063520, 1393746645107232,59147129937893088, 2696314664384853120,131405475202661963520, 6817779852438948837120,375193156508083422581760] |