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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 5 |
| 5 | 20 |
| 6 | 77 |
| 7 | 437 |
| 8 | 5509 |
| 9 | 54475 |
| 10 | 1031232 |
| 11 | 31874836 |
| 12 | 789351469 |
| 13 | 47552777430 |
| 14 | 3302430043985 |
| 15 | 223753995897916 |
| 16 | 39177880844093733 |
| 17 | 5954060239110086680 |
| 18 | 1226026438114057710320 |
| 19 | 551315671593483499670137 |
| 20 | 188615011023291125237647365 |
| 21 | 124995445742889226418307452940 |
[1,1,2,3,5,20,77,437,5509,54475,1031232,31874836, 789351469,47552777430,3302430043985, 223753995897916,39177880844093733, 5954060239110086680,1226026438114057710320, 551315671593483499670137, 188615011023291125237647365, 124995445742889226418307452940] |