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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 0 |
| 3 | 2 |
| 4 | 4 |
| 5 | 12 |
| 6 | 60 |
| 7 | 226 |
| 8 | 1076 |
| 9 | 5156 |
| 10 | 24984 |
| 11 | 128548 |
| 12 | 663040 |
| 13 | 3514968 |
| 14 | 18918792 |
| 15 | 103123906 |
| 16 | 569877652 |
| 17 | 3180066004 |
| 18 | 17921451960 |
| 19 | 101842206548 |
| 20 | 583109887600 |
| 21 | 3361640932872 |
| 22 | 19499226668816 |
[0,2,0,2,4,12,60,226,1076,5156,24984,128548, 663040,3514968,18918792,103123906,569877652, 3180066004,17921451960,101842206548,583109887600, 3361640932872,19499226668816] |