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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 12 |
| 5 | 120 |
| 6 | 780 |
| 7 | 4212 |
| 8 | 20412 |
| 9 | 93360 |
| 10 | 409260 |
| 11 | 1749780 |
| 12 | 7338000 |
| 13 | 30394560 |
| 14 | 124700928 |
| 15 | 508291692 |
| 16 | 2061586800 |
| 17 | 8332140720 |
| 18 | 33585682920 |
| 19 | 135116412660 |
| 20 | 542785390680 |
| 21 | 2178110585388 |
| 22 | 8733343485120 |
[0,0,0,12,120,780,4212,20412,93360,409260,1749780, 7338000,30394560,124700928,508291692,2061586800, 8332140720,33585682920,135116412660,542785390680, 2178110585388,8733343485120] |