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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 27 |
| 5 | 173 |
| 6 | 1464 |
| 7 | 15414 |
| 8 | 193901 |
| 9 | 2834337 |
| 10 | 47182518 |
| 11 | 880910414 |
| 12 | 18225754839 |
| 13 | 413835006621 |
| 14 | 10230048547292 |
| 15 | 273473280803598 |
| 16 | 7860479860630329 |
| 17 | 241731205891735649 |
| 18 | 7919436892637421066 |
| 19 | 275351783014543431222 |
| 20 | 10126387847107625874803 |
| 21 | 392728180939713131370669 |
[1,1,2,6,27,173,1464,15414,193901,2834337, 47182518,880910414,18225754839,413835006621, 10230048547292,273473280803598,7860479860630329, 241731205891735649,7919436892637421066, 275351783014543431222,10126387847107625874803, 392728180939713131370669] |