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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 16 |
| 5 | 74 |
| 6 | 368 |
| 7 | 1776 |
| 8 | 9624 |
| 9 | 57916 |
| 10 | 365502 |
| 11 | 2682244 |
| 12 | 20315800 |
| 13 | 175739338 |
| 14 | 1565766116 |
| 15 | 15452316746 |
| 16 | 156617881640 |
[1,2,6,16,74,368,1776,9624,57916,365502,2682244, 20315800,175739338,1565766116,15452316746, 156617881640] |