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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 18 |
| 3 | 240 |
| 4 | 3850 |
| 5 | 68796 |
| 6 | 1319472 |
| 7 | 26604864 |
| 8 | 556794810 |
| 9 | 11993338500 |
| 10 | 264333180540 |
| 11 | 5935956324480 |
| 12 | 135389270500848 |
| 13 | 3128818447143200 |
| 14 | 73123195376232000 |
| 15 | 1725644509205633280 |
| 16 | 41071074678970154010 |
| 17 | 984853105623747983700 |
| 18 | 23773506148264947574500 |
[1,2,18,240,3850,68796,1319472,26604864,556794810, 11993338500,264333180540,5935956324480, 135389270500848,3128818447143200, 73123195376232000,1725644509205633280, 41071074678970154010,984853105623747983700, 23773506148264947574500] |