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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 4 |
| 4 | 13 |
| 5 | 18 |
| 6 | 40 |
| 7 | 71 |
| 8 | 132 |
| 9 | 231 |
| 10 | 459 |
| 11 | 990 |
| 12 | 2114 |
| 13 | 4237 |
| 14 | 8234 |
| 15 | 16054 |
| 16 | 31280 |
| 17 | 60252 |
| 18 | 115810 |
[1,2,4,4,13,18,40,71,132,231,459,990,2114,4237, 8234,16054,31280,60252,115810] |