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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 7 |
| 2 | 18 |
| 3 | 55 |
| 4 | 144 |
| 5 | 404 |
| 6 | 1060 |
| 7 | 2853 |
| 8 | 7442 |
| 9 | 19573 |
| 10 | 50670 |
| 11 | 131368 |
| 12 | 337622 |
| 13 | 866819 |
| 14 | 2213650 |
| 15 | 5642899 |
| 16 | 14332988 |
| 17 | 36335548 |
| 18 | 91872760 |
| 19 | 231875713 |
| 20 | 584030738 |
| 21 | 1468631153 |
| 22 | 3686943130 |
| 23 | 9242753104 |
| 24 | 23138167146 |
| 25 | 57851432575 |
| 26 | 144470316562 |
| 27 | 360384852207 |
| 28 | 898051760168 |
[2,7,18,55,144,404,1060,2853,7442,19573,50670, 131368,337622,866819,2213650,5642899,14332988, 36335548,91872760,231875713,584030738,1468631153, 3686943130,9242753104,23138167146,57851432575, 144470316562,360384852207,898051760168] |