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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 20 |
| 4 | 316 |
| 5 | 6686 |
| 6 | 173379 |
| 7 | 5255624 |
| 8 | 180911070 |
| 9 | 6938866748 |
| 10 | 292678301988 |
| 11 | 13446616806957 |
| 12 | 668017569348751 |
| 13 | 35678261176871802 |
| 14 | 2038906890461704040 |
| 15 | 124171127134721710130 |
| 16 | 8030684434410398312840 |
| 17 | 549848454475826567644385 |
| 18 | 39744302449387229743134043 |
[1,1,2,20,316,6686,173379,5255624,180911070, 6938866748,292678301988,13446616806957, 668017569348751,35678261176871802, 2038906890461704040,124171127134721710130, 8030684434410398312840,549848454475826567644385, 39744302449387229743134043] |