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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 40 |
| 5 | 264 |
| 6 | 2048 |
| 7 | 18864 |
| 8 | 196992 |
| 9 | 2330112 |
| 10 | 30519552 |
| 11 | 440998656 |
| 12 | 6940852224 |
| 13 | 118501542912 |
| 14 | 2177222879232 |
| 15 | 42886017982464 |
| 16 | 900748014944256 |
| 17 | 20107190510714880 |
| 18 | 475167358873239552 |
| 19 | 11854636521914695680 |
| 20 | 311291779253770911744 |
| 21 | 8583598112533040332800 |
| 22 | 247944624171011289907200 |
[1,1,2,8,40,264,2048,18864,196992,2330112, 30519552,440998656,6940852224,118501542912, 2177222879232,42886017982464,900748014944256, 20107190510714880,475167358873239552, 11854636521914695680,311291779253770911744, 8583598112533040332800,247944624171011289907200] |