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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 5 |
| 4 | 6 |
| 5 | 20 |
| 6 | 31 |
| 7 | 54 |
| 8 | 306 |
| 9 | 356 |
| 10 | 762 |
| 11 | 3174 |
| 12 | 20240 |
| 13 | 22693 |
| 14 | 35793 |
| 15 | 58491 |
| 16 | 81251 |
| 17 | 206410 |
| 18 | 228533 |
| 19 | 3987683 |
| 20 | 5635890 |
[0,1,4,5,6,20,31,54,306,356,762,3174,20240,22693, 35793,58491,81251,206410,228533,3987683,5635890] |