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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 7 |
| 3 | 31 |
| 4 | 172 |
| 5 | 903 |
| 6 | 4859 |
| 7 | 26123 |
| 8 | 141519 |
| 9 | 769915 |
| 10 | 4209720 |
| 11 | 23118268 |
| 12 | 127495912 |
| 13 | 705885128 |
| 14 | 3922515554 |
| 15 | 21871461990 |
| 16 | 122341995397 |
| 17 | 686381562245 |
| 18 | 3861568338064 |
| 19 | 21781724157952 |
| 20 | 123162942539680 |
| 21 | 698010289536681 |
[1,7,31,172,903,4859,26123,141519,769915,4209720, 23118268,127495912,705885128,3922515554, 21871461990,122341995397,686381562245, 3861568338064,21781724157952,123162942539680, 698010289536681] |