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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 8 |
| 3 | 20 |
| 4 | 60 |
| 5 | 204 |
| 6 | 748 |
| 7 | 2860 |
| 8 | 11180 |
| 9 | 44204 |
| 10 | 175788 |
| 11 | 701100 |
| 12 | 2800300 |
| 13 | 11193004 |
| 14 | 44755628 |
| 15 | 178989740 |
| 16 | 715893420 |
| 17 | 2863442604 |
| 18 | 11453508268 |
| 19 | 45813508780 |
| 20 | 183252986540 |
| 21 | 733009849004 |
| 22 | 2932035201708 |
| 23 | 11728132418220 |
| 24 | 46912512895660 |
| 25 | 187650018028204 |
| 26 | 750600005003948 |
| 27 | 3002399885798060 |
[4,8,20,60,204,748,2860,11180,44204,175788,701100, 2800300,11193004,44755628,178989740,715893420, 2863442604,11453508268,45813508780,183252986540, 733009849004,2932035201708,11728132418220, 46912512895660,187650018028204,750600005003948, 3002399885798060] |