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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 33 |
| 5 | 87 |
| 6 | 222 |
| 7 | 550 |
| 8 | 1327 |
| 9 | 3129 |
| 10 | 7236 |
| 11 | 16464 |
| 12 | 36957 |
| 13 | 82027 |
| 14 | 180346 |
| 15 | 393354 |
| 16 | 852123 |
| 17 | 1835181 |
| 18 | 3932352 |
| 19 | 8388820 |
| 20 | 17826025 |
| 21 | 37748991 |
| 22 | 79692054 |
| 23 | 167772462 |
| 24 | 352321863 |
| 25 | 738197857 |
| 26 | 1543504252 |
| 27 | 3221225880 |
| 28 | 6710886837 |
[1,4,12,33,87,222,550,1327,3129,7236,16464,36957, 82027,180346,393354,852123,1835181,3932352, 8388820,17826025,37748991,79692054,167772462, 352321863,738197857,1543504252,3221225880, 6710886837] |