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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 32 |
| 4 | 165 |
| 5 | 840 |
| 6 | 4251 |
| 7 | 21443 |
| 8 | 107946 |
| 9 | 542680 |
| 10 | 2725635 |
| 11 | 13679997 |
| 12 | 68623176 |
| 13 | 344090307 |
| 14 | 1724754180 |
| 15 | 8642952000 |
| 16 | 43300971885 |
| 17 | 216895107480 |
| 18 | 1086253033035 |
| 19 | 5439405705125 |
| 20 | 27234492215400 |
| 21 | 136345625309965 |
| 22 | 682531666024170 |
[0,1,6,32,165,840,4251,21443,107946,542680, 2725635,13679997,68623176,344090307,1724754180, 8642952000,43300971885,216895107480,1086253033035, 5439405705125,27234492215400,136345625309965, 682531666024170] |