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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 6 |
| 3 | 48 |
| 4 | 438 |
| 5 | 3936 |
| 6 | 35430 |
| 7 | 318864 |
| 8 | 2869782 |
| 9 | 25828032 |
| 10 | 232452294 |
| 11 | 2092070640 |
| 12 | 18828635766 |
| 13 | 169457721888 |
| 14 | 1525119496998 |
| 15 | 13726075472976 |
| 16 | 123534679256790 |
| 17 | 1111812113311104 |
| 18 | 10006309019799942 |
| 19 | 90056781178199472 |
| 20 | 810511030603795254 |
[0,6,48,438,3936,35430,318864,2869782,25828032, 232452294,2092070640,18828635766,169457721888, 1525119496998,13726075472976,123534679256790, 1111812113311104,10006309019799942, 90056781178199472,810511030603795254] |