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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 6 |
| 4 | 20 |
| 5 | 70 |
| 6 | 302 |
| 7 | 1386 |
| 8 | 6902 |
| 9 | 35862 |
| 10 | 194202 |
| 11 | 1082642 |
| 12 | 6191680 |
| 13 | 36141118 |
| 14 | 214715244 |
| 15 | 1294849186 |
| 16 | 7911159522 |
| 17 | 48888093910 |
| 18 | 305165808290 |
| 19 | 1921992409066 |
| 20 | 12202404037088 |
| 21 | 78031629139246 |
| 22 | 502263432618224 |
| 23 | 3252160882871210 |
[1,1,3,6,20,70,302,1386,6902,35862,194202,1082642, 6191680,36141118,214715244,1294849186,7911159522, 48888093910,305165808290,1921992409066, 12202404037088,78031629139246,502263432618224, 3252160882871210] |