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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 73 |
| 5 | 301 |
| 6 | 1561 |
| 7 | 32131 |
| 8 | 306097 |
| 9 | 2062873 |
| 10 | 43102801 |
| 11 | 720515071 |
| 12 | 7245589561 |
| 13 | 136364378437 |
| 14 | 3259345980073 |
| 15 | 47903339552251 |
| 16 | 873735377165281 |
| 17 | 25383884535029041 |
| 18 | 515592396859327777 |
| 19 | 10003196649764818423 |
| 20 | 316630570292623967401 |
| 21 | 8359224513085985870941 |
[1,1,1,7,73,301,1561,32131,306097,2062873, 43102801,720515071,7245589561,136364378437, 3259345980073,47903339552251,873735377165281, 25383884535029041,515592396859327777, 10003196649764818423,316630570292623967401, 8359224513085985870941] |