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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 6 |
| 3 | 21 |
| 4 | 77 |
| 5 | 212 |
| 6 | 542 |
| 7 | 1270 |
| 8 | 2830 |
| 9 | 6043 |
| 10 | 12503 |
| 11 | 25208 |
| 12 | 49772 |
| 13 | 96572 |
| 14 | 184646 |
| 15 | 348641 |
| 16 | 651201 |
| 17 | 1204908 |
| 18 | 2211018 |
| 19 | 4027570 |
| 20 | 7288750 |
| 21 | 13113415 |
| 22 | 23468331 |
| 23 | 41799216 |
| 24 | 74124312 |
| 25 | 130925112 |
| 26 | 230408262 |
| 27 | 404121645 |
| 28 | 706605365 |
| 29 | 1231946948 |
| 30 | 2142132278 |
[0,6,21,77,212,542,1270,2830,6043,12503,25208, 49772,96572,184646,348641,651201,1204908,2211018, 4027570,7288750,13113415,23468331,41799216, 74124312,130925112,230408262,404121645,706605365, 1231946948,2142132278] |