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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 15 |
| 4 | 54 |
| 5 | 118 |
| 6 | 471 |
| 7 | 973 |
| 8 | 4128 |
| 9 | 8262 |
| 10 | 36481 |
| 11 | 71534 |
| 12 | 324876 |
| 13 | 627926 |
| 14 | 2911923 |
| 15 | 5568348 |
| 16 | 26241376 |
| 17 | 49767432 |
| 18 | 237550401 |
| 19 | 447567059 |
| 20 | 2158650078 |
| 21 | 4045351674 |
| 22 | 19679880649 |
| 23 | 36716551814 |
| 24 | 179920446576 |
| 25 | 334415846660 |
[1,2,6,15,54,118,471,973,4128,8262,36481,71534, 324876,627926,2911923,5568348,26241376,49767432, 237550401,447567059,2158650078,4045351674, 19679880649,36716551814,179920446576,334415846660] |