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| n | a(n) |
|---|---|
| 1 | 15 |
| 2 | 105 |
| 3 | 647 |
| 4 | 3728 |
| 5 | 20656 |
| 6 | 111222 |
| 7 | 586908 |
| 8 | 3047226 |
| 9 | 15620118 |
| 10 | 79228317 |
| 11 | 398364306 |
| 12 | 1988133262 |
| 13 | 9858922561 |
| 14 | 48617189158 |
| 15 | 238575216150 |
| 16 | 1165684780558 |
| 17 | 5673701149975 |
| 18 | 27520684819357 |
| 19 | 133080240201400 |
| 20 | 641746039540686 |
[15,105,647,3728,20656,111222,586908,3047226, 15620118,79228317,398364306,1988133262,9858922561, 48617189158,238575216150,1165684780558, 5673701149975,27520684819357,133080240201400, 641746039540686] |