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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 55 |
| 4 | 600 |
| 5 | 7946 |
| 6 | 123480 |
| 7 | 2208492 |
| 8 | 44710272 |
| 9 | 1011177360 |
| 10 | 25274905920 |
| 11 | 692042185440 |
| 12 | 20602098316800 |
| 13 | 662620120237440 |
| 14 | 22898921925035520 |
| 15 | 846245264387040000 |
| 16 | 33303963647943475200 |
| 17 | 1390631677349880268800 |
| 18 | 61407154400075559936000 |
| 19 | 2859166138267857522585600 |
[1,6,55,600,7946,123480,2208492,44710272, 1011177360,25274905920,692042185440, 20602098316800,662620120237440,22898921925035520, 846245264387040000,33303963647943475200, 1390631677349880268800,61407154400075559936000, 2859166138267857522585600] |