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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 15 |
| 4 | 101 |
| 5 | 980 |
| 6 | 12202 |
| 7 | 184821 |
| 8 | 3297457 |
| 9 | 67731334 |
| 10 | 1574304986 |
| 11 | 40851766527 |
| 12 | 1170684360925 |
| 13 | 36720042483592 |
| 14 | 1251308658130546 |
| 15 | 46034015337733481 |
| 16 | 1818399978159990977 |
| 17 | 76762718946972480010 |
| 18 | 3448810852242967123282 |
[2,4,15,101,980,12202,184821,3297457,67731334, 1574304986,40851766527,1170684360925, 36720042483592,1251308658130546,46034015337733481, 1818399978159990977,76762718946972480010, 3448810852242967123282] |