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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 68 |
| 5 | 710 |
| 6 | 9414 |
| 7 | 151032 |
| 8 | 2840648 |
| 9 | 61247664 |
| 10 | 1488691530 |
| 11 | 40262372480 |
| 12 | 1199047315212 |
| 13 | 38984874829056 |
| 14 | 1373954963380622 |
| 15 | 52171222364513280 |
| 16 | 2123286652815757200 |
| 17 | 92201888436661409792 |
| 18 | 4255016114128163220882 |
| 19 | 207954945060162884960256 |
[0,1,2,9,68,710,9414,151032,2840648,61247664, 1488691530,40262372480,1199047315212, 38984874829056,1373954963380622,52171222364513280, 2123286652815757200,92201888436661409792, 4255016114128163220882,207954945060162884960256] |