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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 67 |
| 5 | 223 |
| 6 | 740 |
| 7 | 2454 |
| 8 | 8138 |
| 9 | 26989 |
| 10 | 89509 |
| 11 | 296858 |
| 12 | 984534 |
| 13 | 3265220 |
| 14 | 10829143 |
| 15 | 35914987 |
| 16 | 119112500 |
| 17 | 395038086 |
| 18 | 1310148722 |
| 19 | 4345124521 |
| 20 | 14410659481 |
| 21 | 47793131282 |
| 22 | 158506513926 |
| 23 | 525688823540 |
| 24 | 1743453517147 |
| 25 | 5782185259303 |
| 26 | 19176689280260 |
| 27 | 63599728348374 |
[1,2,6,20,67,223,740,2454,8138,26989,89509,296858, 984534,3265220,10829143,35914987,119112500, 395038086,1310148722,4345124521,14410659481, 47793131282,158506513926,525688823540, 1743453517147,5782185259303,19176689280260, 63599728348374] |