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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 16 |
| 5 | 80 |
| 6 | 400 |
| 7 | 2800 |
| 8 | 22400 |
| 9 | 179200 |
| 10 | 1792000 |
| 11 | 19712000 |
| 12 | 216832000 |
| 13 | 2818816000 |
| 14 | 39463424000 |
| 15 | 552487936000 |
| 16 | 8839806976000 |
| 17 | 150276718592000 |
| 18 | 2554704216064000 |
| 19 | 48539380105216000 |
| 20 | 970787602104320000 |
| 21 | 19415752042086400000 |
| 22 | 427146544925900800000 |
| 23 | 9824370533295718400000 |
| 24 | 225960522265801523200000 |
| 25 | 5649013056645038080000000 |
| 26 | 146874339472770990080000000 |
| 27 | 3818732827816549381939200000 |
[1,1,2,4,16,80,400,2800,22400,179200,1792000, 19712000,216832000,2818816000,39463424000, 552487936000,8839806976000,150276718592000, 2554704216064000,48539380105216000, 970787602104320000,19415752042086400000, 427146544925900800000,9824370533295718400000, 225960522265801523200000, 5649013056645038080000000, 146874339472770990080000000, 3818732827816549381939200000] |