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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 18 |
| 3 | 90 |
| 4 | 423 |
| 5 | 1958 |
| 6 | 9233 |
| 7 | 43725 |
| 8 | 206269 |
| 9 | 971794 |
| 10 | 4583164 |
| 11 | 21622807 |
| 12 | 101988408 |
| 13 | 481001317 |
| 14 | 2268654909 |
| 15 | 10700463129 |
| 16 | 50469641870 |
| 17 | 238042556300 |
| 18 | 1122743524739 |
| 19 | 5295505220276 |
| 20 | 24976631418525 |
| 21 | 117804014337453 |
| 22 | 555630918690165 |
[4,18,90,423,1958,9233,43725,206269,971794, 4583164,21622807,101988408,481001317,2268654909, 10700463129,50469641870,238042556300, 1122743524739,5295505220276,24976631418525, 117804014337453,555630918690165] |