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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 28 |
| 3 | 111 |
| 4 | 550 |
| 5 | 2769 |
| 6 | 13338 |
| 7 | 66012 |
| 8 | 326010 |
| 9 | 1605094 |
| 10 | 7924940 |
| 11 | 39109123 |
| 12 | 192971113 |
| 13 | 952409721 |
| 14 | 4700295351 |
| 15 | 23196736485 |
| 16 | 114482463703 |
| 17 | 564998794109 |
| 18 | 2788411309415 |
| 19 | 13761538059788 |
| 20 | 67916728397389 |
| 21 | 335186625133799 |
[4,28,111,550,2769,13338,66012,326010,1605094, 7924940,39109123,192971113,952409721,4700295351, 23196736485,114482463703,564998794109, 2788411309415,13761538059788,67916728397389, 335186625133799] |