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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 69 |
| 6 | 243 |
| 7 | 869 |
| 8 | 3145 |
| 9 | 11491 |
| 10 | 42312 |
| 11 | 156807 |
| 12 | 584288 |
| 13 | 2187298 |
| 14 | 8221257 |
| 15 | 31009841 |
| 16 | 117331070 |
| 17 | 445174418 |
| 18 | 1693270531 |
| 19 | 6454992143 |
| 20 | 24657428519 |
| 21 | 94363587324 |
| 22 | 361741068087 |
| 23 | 1388892123038 |
| 24 | 5340282880156 |
| 25 | 20560742443041 |
| 26 | 79259430563491 |
| 27 | 305889059254747 |
[1,1,2,6,20,69,243,869,3145,11491,42312,156807, 584288,2187298,8221257,31009841,117331070, 445174418,1693270531,6454992143,24657428519, 94363587324,361741068087,1388892123038, 5340282880156,20560742443041,79259430563491, 305889059254747] |