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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 20 |
| 3 | 152 |
| 4 | 1136 |
| 5 | 8480 |
| 6 | 63296 |
| 7 | 472448 |
| 8 | 3526400 |
| 9 | 26321408 |
| 10 | 196465664 |
| 11 | 1466439680 |
| 12 | 10945654784 |
| 13 | 81699479552 |
| 14 | 609813217280 |
| 15 | 4551707820032 |
| 16 | 33974409691136 |
| 17 | 253588446248960 |
| 18 | 1892809931227136 |
| 19 | 14128125664821248 |
| 20 | 105453765593661440 |
[2,20,152,1136,8480,63296,472448,3526400,26321408, 196465664,1466439680,10945654784,81699479552, 609813217280,4551707820032,33974409691136, 253588446248960,1892809931227136, 14128125664821248,105453765593661440] |