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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 27 |
| 5 | 172 |
| 6 | 1508 |
| 7 | 18107 |
| 8 | 297532 |
| 9 | 6694132 |
| 10 | 206841391 |
| 11 | 8816277300 |
| 12 | 520844677834 |
| 13 | 42854370882379 |
| 14 | 4933351077116176 |
| 15 | 797908056582772334 |
| 16 | 181972606629594221271 |
| 17 | 58701383528452842764544 |
| 18 | 26853636463946258949427440 |
| 19 | 17457976736153040916394583563 |
[1,1,2,6,27,172,1508,18107,297532,6694132, 206841391,8816277300,520844677834,42854370882379, 4933351077116176,797908056582772334, 181972606629594221271,58701383528452842764544, 26853636463946258949427440, 17457976736153040916394583563] |