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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 36 |
| 3 | 250 |
| 4 | 2040 |
| 5 | 19334 |
| 6 | 209580 |
| 7 | 2562354 |
| 8 | 34915680 |
| 9 | 524986462 |
| 10 | 8636859924 |
| 11 | 154357103498 |
| 12 | 2978418173640 |
| 13 | 61718786864310 |
| 14 | 1367098836863868 |
| 15 | 32236969655283682 |
| 16 | 806313056758966320 |
| 17 | 21322699350055313678 |
| 18 | 594440128269066768612 |
| 19 | 17424632249851351374906 |
[1,6,36,250,2040,19334,209580,2562354,34915680, 524986462,8636859924,154357103498,2978418173640, 61718786864310,1367098836863868,32236969655283682, 806313056758966320,21322699350055313678, 594440128269066768612,17424632249851351374906] |