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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 15 |
| 3 | 248 |
| 4 | 4305 |
| 5 | 76255 |
| 6 | 1361520 |
| 7 | 24384737 |
| 8 | 437245935 |
| 9 | 7843863784 |
| 10 | 140737371825 |
| 11 | 2525326494911 |
| 12 | 45314438127840 |
| 13 | 813129752279233 |
| 14 | 14590988151618255 |
| 15 | 261824431125415640 |
| 16 | 4698247224097107345 |
| 17 | 84306614992412658847 |
| 18 | 1512820749915870503760 |
| 19 | 27146466385039244529569 |
[1,15,248,4305,76255,1361520,24384737,437245935, 7843863784,140737371825,2525326494911, 45314438127840,813129752279233,14590988151618255, 261824431125415640,4698247224097107345, 84306614992412658847,1512820749915870503760, 27146466385039244529569] |