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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 12 |
| 3 | 33 |
| 4 | 87 |
| 5 | 223 |
| 6 | 559 |
| 7 | 1375 |
| 8 | 3327 |
| 9 | 7935 |
| 10 | 18687 |
| 11 | 43519 |
| 12 | 100351 |
| 13 | 229375 |
| 14 | 520191 |
| 15 | 1171455 |
| 16 | 2621439 |
| 17 | 5832703 |
| 18 | 12910591 |
| 19 | 28442623 |
| 20 | 62390271 |
| 21 | 136314879 |
| 22 | 296747007 |
| 23 | 643825663 |
| 24 | 1392508927 |
| 25 | 3003121663 |
| 26 | 6459228159 |
| 27 | 13857980415 |
| 28 | 29662117887 |
| 29 | 63350767615 |
[4,12,33,87,223,559,1375,3327,7935,18687,43519, 100351,229375,520191,1171455,2621439,5832703, 12910591,28442623,62390271,136314879,296747007, 643825663,1392508927,3003121663,6459228159, 13857980415,29662117887,63350767615] |