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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 4 |
| 3 | 6 |
| 4 | 6 |
| 5 | 26 |
| 6 | 90 |
| 7 | 222 |
| 8 | 674 |
| 9 | 2158 |
| 10 | 6546 |
| 11 | 20382 |
| 12 | 63922 |
| 13 | 200946 |
| 14 | 639554 |
| 15 | 2037050 |
| 16 | 6507122 |
| 17 | 20923918 |
| 18 | 67445362 |
| 19 | 217924638 |
| 20 | 706488874 |
| 21 | 2295658074 |
| 22 | 7475460546 |
| 23 | 24394962306 |
| 24 | 79753388458 |
| 25 | 261182132074 |
| 26 | 856719190626 |
| 27 | 2814241452698 |
[4,4,6,6,26,90,222,674,2158,6546,20382,63922, 200946,639554,2037050,6507122,20923918,67445362, 217924638,706488874,2295658074,7475460546, 24394962306,79753388458,261182132074,856719190626, 2814241452698] |