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| n | a(n) |
|---|---|
| 1 | 15 |
| 2 | 225 |
| 3 | 611 |
| 4 | 1805 |
| 5 | 6235 |
| 6 | 22995 |
| 7 | 89815 |
| 8 | 361261 |
| 9 | 1483295 |
| 10 | 6161925 |
| 11 | 25792655 |
| 12 | 108453119 |
| 13 | 457324951 |
| 14 | 1931799849 |
| 15 | 8168996779 |
| 16 | 34567178365 |
| 17 | 146331546515 |
| 18 | 619615536891 |
| 19 | 2624066727095 |
| 20 | 11113979515925 |
| 21 | 47075003890759 |
[15,225,611,1805,6235,22995,89815,361261,1483295, 6161925,25792655,108453119,457324951,1931799849, 8168996779,34567178365,146331546515,619615536891, 2624066727095,11113979515925,47075003890759] |