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| n | a(n) |
|---|---|
| 1 | 400 |
| 2 | 3000 |
| 3 | 22500 |
| 4 | 105000 |
| 5 | 490000 |
| 6 | 1715000 |
| 7 | 6002500 |
| 8 | 17287200 |
| 9 | 49787136 |
| 10 | 124467840 |
| 11 | 311169600 |
| 12 | 698544000 |
| 13 | 1568160000 |
| 14 | 3234330000 |
| 15 | 6670805625 |
| 16 | 12847477500 |
| 17 | 24743290000 |
| 18 | 45032787800 |
| 19 | 81959673796 |
| 20 | 142244061960 |
[400,3000,22500,105000,490000,1715000,6002500, 17287200,49787136,124467840,311169600,698544000, 1568160000,3234330000,6670805625,12847477500, 24743290000,45032787800,81959673796,142244061960] |