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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 18 |
| 3 | 31 |
| 4 | 170 |
| 5 | 792 |
| 6 | 3759 |
| 7 | 18897 |
| 8 | 91138 |
| 9 | 476043 |
| 10 | 2434631 |
| 11 | 12363865 |
| 12 | 63517567 |
| 13 | 326131379 |
| 14 | 1671754689 |
| 15 | 8572647264 |
| 16 | 44017843069 |
| 17 | 225847266812 |
| 18 | 1158829313595 |
| 19 | 5947763981588 |
| 20 | 30523170292757 |
| 21 | 156640465674701 |
| 22 | 803891068081321 |
[0,18,31,170,792,3759,18897,91138,476043,2434631, 12363865,63517567,326131379,1671754689,8572647264, 44017843069,225847266812,1158829313595, 5947763981588,30523170292757,156640465674701, 803891068081321] |