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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 16 |
| 5 | 104 |
| 6 | 688 |
| 7 | 4976 |
| 8 | 40192 |
| 9 | 362624 |
| 10 | 3628288 |
| 11 | 39915776 |
| 12 | 478999552 |
| 13 | 6227016704 |
| 14 | 87178283008 |
| 15 | 1307674351616 |
| 16 | 20922789855232 |
| 17 | 355687428030464 |
| 18 | 6402373705596928 |
| 19 | 121645100408569856 |
| 20 | 2432902008176115712 |
| 21 | 51090942171708391424 |
| 22 | 1124000727777605582848 |
[0,0,0,2,16,104,688,4976,40192,362624,3628288, 39915776,478999552,6227016704,87178283008, 1307674351616,20922789855232,355687428030464, 6402373705596928,121645100408569856, 2432902008176115712,51090942171708391424, 1124000727777605582848] |