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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 28 |
| 3 | 141 |
| 4 | 629 |
| 5 | 2645 |
| 6 | 10821 |
| 7 | 43741 |
| 8 | 175845 |
| 9 | 705101 |
| 10 | 2823797 |
| 11 | 11301917 |
| 12 | 45221061 |
| 13 | 180910957 |
| 14 | 723697173 |
| 15 | 2894895293 |
[1,4,28,141,629,2645,10821,43741,175845,705101, 2823797,11301917,45221061,180910957,723697173, 2894895293] |