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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 121 |
| 6 | 751 |
| 7 | 7351 |
| 8 | 73417 |
| 9 | 749449 |
| 10 | 9477181 |
| 11 | 136883341 |
| 12 | 2041250641 |
| 13 | 33289802833 |
| 14 | 608025141907 |
| 15 | 11815916748091 |
| 16 | 242532915013201 |
| 17 | 5369303859003601 |
| 18 | 126896359555326745 |
| 19 | 3153096762426186553 |
| 20 | 82705881733348530241 |
| 21 | 2293511922269658189121 |
[1,1,1,4,25,121,751,7351,73417,749449,9477181, 136883341,2041250641,33289802833,608025141907, 11815916748091,242532915013201,5369303859003601, 126896359555326745,3153096762426186553, 82705881733348530241,2293511922269658189121] |