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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 441 |
| 3 | 2307 |
| 4 | 19909 |
| 5 | 137719 |
| 6 | 1048423 |
| 7 | 7666319 |
| 8 | 57113109 |
| 9 | 422082891 |
| 10 | 3130112351 |
| 11 | 23173976223 |
| 12 | 171676789835 |
| 13 | 1271417316909 |
| 14 | 9417475398607 |
| 15 | 69753625991829 |
| 16 | 516671332697659 |
| 17 | 3826965495103137 |
| 18 | 28346096345105751 |
| 19 | 209956452832167033 |
[21,441,2307,19909,137719,1048423,7666319, 57113109,422082891,3130112351,23173976223, 171676789835,1271417316909,9417475398607, 69753625991829,516671332697659,3826965495103137, 28346096345105751,209956452832167033] |