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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 46 |
| 5 | 160 |
| 6 | 559 |
| 7 | 1951 |
| 8 | 6811 |
| 9 | 23776 |
| 10 | 82999 |
| 11 | 289738 |
| 12 | 1011436 |
| 13 | 3530785 |
| 14 | 12325489 |
| 15 | 43026601 |
| 16 | 150199996 |
| 17 | 524327701 |
| 18 | 1830356494 |
| 19 | 6389524888 |
| 20 | 22304959951 |
| 21 | 77863573135 |
| 22 | 271811114419 |
| 23 | 948855529576 |
| 24 | 3312325244431 |
| 25 | 11562875678026 |
| 26 | 40364421993364 |
| 27 | 140906692091713 |
[1,4,13,46,160,559,1951,6811,23776,82999,289738, 1011436,3530785,12325489,43026601,150199996, 524327701,1830356494,6389524888,22304959951, 77863573135,271811114419,948855529576, 3312325244431,11562875678026,40364421993364, 140906692091713] |