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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 40 |
| 3 | 332 |
| 4 | 2672 |
| 5 | 21396 |
| 6 | 171192 |
| 7 | 1369564 |
| 8 | 10956544 |
| 9 | 87652388 |
| 10 | 701219144 |
| 11 | 5609753196 |
| 12 | 44878025616 |
| 13 | 359024204980 |
| 14 | 2872193639896 |
| 15 | 22977549119228 |
| 16 | 183820392953888 |
| 17 | 1470563143631172 |
| 18 | 11764505149049448 |
| 19 | 94116041192395660 |
[0,4,40,332,2672,21396,171192,1369564,10956544, 87652388,701219144,5609753196,44878025616, 359024204980,2872193639896,22977549119228, 183820392953888,1470563143631172, 11764505149049448,94116041192395660] |