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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 6 |
| 4 | 18 |
| 5 | 33 |
| 6 | 53 |
| 7 | 77 |
| 8 | 89 |
| 9 | 212 |
| 10 | 306 |
| 11 | 701 |
| 12 | 1455 |
| 13 | 2138 |
| 14 | 2213 |
| 15 | 3065 |
| 16 | 9299 |
| 17 | 16439 |
| 18 | 16893 |
| 19 | 28574 |
| 20 | 54050 |
[0,3,6,18,33,53,77,89,212,306,701,1455,2138,2213, 3065,9299,16439,16893,28574,54050] |