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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 18 |
| 4 | 66 |
| 5 | 250 |
| 6 | 998 |
| 7 | 4010 |
| 8 | 16537 |
| 9 | 69342 |
| 10 | 293458 |
| 11 | 1257093 |
| 12 | 5424876 |
| 13 | 23588068 |
| 14 | 103233879 |
| 15 | 454308177 |
| 16 | 2009507717 |
| 17 | 8926272795 |
| 18 | 39812543051 |
| 19 | 178190481133 |
| 20 | 800159369179 |
| 21 | 3603867667219 |
| 22 | 16274928666567 |
| 23 | 73684182750185 |
| 24 | 334362668167067 |
| 25 | 1520532623466630 |
| 26 | 6928507283774292 |
| 27 | 31628926838053398 |
[1,2,5,18,66,250,998,4010,16537,69342,293458, 1257093,5424876,23588068,103233879,454308177, 2009507717,8926272795,39812543051,178190481133, 800159369179,3603867667219,16274928666567, 73684182750185,334362668167067,1520532623466630, 6928507283774292,31628926838053398] |