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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 51 |
| 4 | 168 |
| 5 | 540 |
| 6 | 1711 |
| 7 | 5365 |
| 8 | 16698 |
| 9 | 51679 |
| 10 | 159250 |
| 11 | 489048 |
| 12 | 1497681 |
| 13 | 4576140 |
| 14 | 13955895 |
| 15 | 42493677 |
| 16 | 129211818 |
| 17 | 392441049 |
| 18 | 1190716836 |
| 19 | 3609608838 |
| 20 | 10933915743 |
| 21 | 33097421223 |
| 22 | 100126350090 |
| 23 | 302737691646 |
| 24 | 914897836063 |
[1,4,15,51,168,540,1711,5365,16698,51679,159250, 489048,1497681,4576140,13955895,42493677, 129211818,392441049,1190716836,3609608838, 10933915743,33097421223,100126350090,302737691646, 914897836063] |