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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 13 |
| 3 | 37 |
| 4 | 99 |
| 5 | 254 |
| 6 | 636 |
| 7 | 1567 |
| 8 | 3822 |
| 9 | 9261 |
| 10 | 22346 |
| 11 | 53773 |
| 12 | 129174 |
| 13 | 309958 |
| 14 | 743228 |
| 15 | 1781330 |
| 16 | 4268166 |
| 17 | 10224885 |
| 18 | 24492034 |
| 19 | 58662298 |
| 20 | 140498877 |
| 21 | 336491169 |
| 22 | 805872377 |
| 23 | 1929983778 |
| 24 | 4622083068 |
| 25 | 11069289411 |
| 26 | 26509431448 |
| 27 | 63486333364 |
[1,4,13,37,99,254,636,1567,3822,9261,22346,53773, 129174,309958,743228,1781330,4268166,10224885, 24492034,58662298,140498877,336491169,805872377, 1929983778,4622083068,11069289411,26509431448, 63486333364] |