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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 6 |
| 3 | 10 |
| 4 | 15 |
| 5 | 21 |
| 6 | 28 |
| 7 | 45 |
| 8 | 55 |
| 9 | 78 |
| 10 | 91 |
| 11 | 105 |
| 12 | 136 |
| 13 | 406 |
| 14 | 496 |
| 15 | 528 |
| 16 | 595 |
| 17 | 703 |
| 18 | 741 |
| 19 | 1035 |
| 20 | 1081 |
| 21 | 1225 |
[3,6,10,15,21,28,45,55,78,91,105,136,406,496,528, 595,703,741,1035,1081,1225] |