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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 64 |
| 3 | 1920 |
| 4 | 86464 |
| 5 | 5304320 |
| 6 | 418131456 |
| 7 | 40727959552 |
| 8 | 4765747597312 |
| 9 | 655794545577984 |
| 10 | 104360850604687360 |
| 11 | 18948720298674028544 |
| 12 | 3882059495694122090496 |
| 13 | 889053986706845142876160 |
| 14 | 225799026538694916941283328 |
| 15 | 63163063632830911303738982400 |
| 16 | 19344290761718462120859544846336 |
| 17 | 6452149866509553556278434299117568 |
| 18 | 2332867461867950308492384248149311488 |
| 19 | 910538103145382496893587688740637114368 |
| 20 | 382208425560563535419125500691963382333440 |
[1,4,64,1920,86464,5304320,418131456,40727959552, 4765747597312,655794545577984,104360850604687360, 18948720298674028544,3882059495694122090496, 889053986706845142876160, 225799026538694916941283328, 63163063632830911303738982400, 19344290761718462120859544846336, 6452149866509553556278434299117568, 2332867461867950308492384248149311488, 910538103145382496893587688740637114368, 382208425560563535419125500691963382333440] |