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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 62 |
| 4 | 237 |
| 5 | 901 |
| 6 | 3418 |
| 7 | 12956 |
| 8 | 49096 |
| 9 | 186029 |
| 10 | 704861 |
| 11 | 2670692 |
| 12 | 10119152 |
| 13 | 38341126 |
| 14 | 145273353 |
| 15 | 550436561 |
| 16 | 2085588866 |
| 17 | 7902239404 |
| 18 | 29941371656 |
| 19 | 113447051497 |
| 20 | 429847830217 |
| 21 | 1628681887876 |
| 22 | 6171031956688 |
| 23 | 23381874459566 |
| 24 | 88593294803061 |
| 25 | 335677616363629 |
[1,4,16,62,237,901,3418,12956,49096,186029,704861, 2670692,10119152,38341126,145273353,550436561, 2085588866,7902239404,29941371656,113447051497, 429847830217,1628681887876,6171031956688, 23381874459566,88593294803061,335677616363629] |