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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 15 |
| 5 | 181 |
| 6 | 2163 |
| 7 | 27133 |
| 8 | 364395 |
| 9 | 5272861 |
| 10 | 82289163 |
| 11 | 1383131773 |
| 12 | 24978057195 |
| 13 | 483269202781 |
| 14 | 9987505786443 |
| 15 | 219821796033853 |
| 16 | 5137810967933355 |
| 17 | 127169580176271901 |
| 18 | 3324712113052429323 |
| 19 | 91585136315240091133 |
| 20 | 2652142325158529483115 |
| 21 | 80562824634615270041821 |
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