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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 32 |
| 4 | 368 |
| 5 | 5656 |
| 6 | 109024 |
| 7 | 2533712 |
| 8 | 68995328 |
| 9 | 2155513216 |
| 10 | 76014982144 |
| 11 | 2987332904192 |
| 12 | 129473128921088 |
| 13 | 6135478762187776 |
| 14 | 315609465774936064 |
| 15 | 17515027337549545472 |
| 16 | 1043104219010147483648 |
| 17 | 66358462250378681614336 |
| 18 | 4491141928841064201846784 |
| 19 | 322219449242531127348887552 |
[1,1,4,32,368,5656,109024,2533712,68995328, 2155513216,76014982144,2987332904192, 129473128921088,6135478762187776, 315609465774936064,17515027337549545472, 1043104219010147483648,66358462250378681614336, 4491141928841064201846784, 322219449242531127348887552] |