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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 60 |
| 3 | 1120 |
| 4 | 24220 |
| 5 | 567504 |
| 6 | 14030016 |
| 7 | 360222720 |
| 8 | 9513014940 |
| 9 | 256758913840 |
| 10 | 7051260776560 |
| 11 | 196403499277440 |
| 12 | 5535202897806400 |
| 13 | 157551884911456000 |
| 14 | 4522682234563776000 |
| 15 | 130783762623673221120 |
| 16 | 3806221127760278029980 |
[1,4,60,1120,24220,567504,14030016,360222720, 9513014940,256758913840,7051260776560, 196403499277440,5535202897806400, 157551884911456000,4522682234563776000, 130783762623673221120,3806221127760278029980] |