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| n | a(n) |
|---|---|
| 0 | 3 |
| 1 | 22 |
| 2 | 140 |
| 3 | 856 |
| 4 | 5168 |
| 5 | 31072 |
| 6 | 186560 |
| 7 | 1119616 |
| 8 | 6718208 |
| 9 | 40310272 |
| 10 | 241863680 |
| 11 | 1451186176 |
| 12 | 8707125248 |
| 13 | 52242767872 |
| 14 | 313456640000 |
| 15 | 1880739905536 |
| 16 | 11284439564288 |
| 17 | 67706637647872 |
| 18 | 406239826411520 |
| 19 | 2437438959517696 |
| 20 | 14624633759203328 |
| 21 | 87747802559414272 |
[3,22,140,856,5168,31072,186560,1119616,6718208, 40310272,241863680,1451186176,8707125248, 52242767872,313456640000,1880739905536, 11284439564288,67706637647872,406239826411520, 2437438959517696,14624633759203328, 87747802559414272] |