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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 21 |
| 5 | 73 |
| 6 | 236 |
| 7 | 705 |
| 8 | 1970 |
| 9 | 5224 |
| 10 | 13307 |
| 11 | 32866 |
| 12 | 79251 |
| 13 | 187523 |
| 14 | 437030 |
| 15 | 1005935 |
| 16 | 2291536 |
| 17 | 5174458 |
| 18 | 11596189 |
| 19 | 25816552 |
| 20 | 57141641 |
| 21 | 125822061 |
| 22 | 275766912 |
| 23 | 601872301 |
| 24 | 1308610526 |
| 25 | 2835334908 |
| 26 | 6123666671 |
| 27 | 13186871710 |
| 28 | 28319917295 |
[1,2,6,21,73,236,705,1970,5224,13307,32866,79251, 187523,437030,1005935,2291536,5174458,11596189, 25816552,57141641,125822061,275766912,601872301, 1308610526,2835334908,6123666671,13186871710, 28319917295] |