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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 18 |
| 3 | 78 |
| 4 | 329 |
| 5 | 1396 |
| 6 | 5925 |
| 7 | 25147 |
| 8 | 106731 |
| 9 | 452984 |
| 10 | 1922547 |
| 11 | 8159665 |
| 12 | 34631193 |
| 13 | 146981443 |
| 14 | 623817540 |
| 15 | 2647601755 |
| 16 | 11236931619 |
| 17 | 47691701338 |
| 18 | 202412762994 |
| 19 | 859078738551 |
| 20 | 3646095572825 |
| 21 | 15474731627673 |
| 22 | 65677740521441 |
[4,18,78,329,1396,5925,25147,106731,452984, 1922547,8159665,34631193,146981443,623817540, 2647601755,11236931619,47691701338,202412762994, 859078738551,3646095572825,15474731627673, 65677740521441] |