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| n | a(n) |
|---|---|
| 1 | 21 |
| 2 | 309 |
| 3 | 1621 |
| 4 | 6125 |
| 5 | 42613 |
| 6 | 248303 |
| 7 | 1724088 |
| 8 | 13731628 |
| 9 | 97119162 |
| 10 | 756707222 |
| 11 | 6200379979 |
| 12 | 47495092665 |
| 13 | 381529656480 |
| 14 | 3147373531932 |
| 15 | 24939108924275 |
| 16 | 202897330702581 |
| 17 | 1669347485119689 |
| 18 | 13414358001681700 |
| 19 | 109481811441992527 |
[21,309,1621,6125,42613,248303,1724088,13731628, 97119162,756707222,6200379979,47495092665, 381529656480,3147373531932,24939108924275, 202897330702581,1669347485119689, 13414358001681700,109481811441992527] |