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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 12 |
| 4 | 48 |
| 5 | 144 |
| 6 | 468 |
| 7 | 1404 |
| 8 | 4320 |
| 9 | 12960 |
| 10 | 39204 |
| 11 | 117612 |
| 12 | 353808 |
| 13 | 1061424 |
| 14 | 3187188 |
| 15 | 9561564 |
| 16 | 28693440 |
| 17 | 86080320 |
| 18 | 258267204 |
| 19 | 774801612 |
| 20 | 2324483568 |
| 21 | 6973450704 |
| 22 | 20920588308 |
| 23 | 62761764924 |
| 24 | 188286003360 |
| 25 | 564858010080 |
| 26 | 1694576156004 |
[0,4,12,48,144,468,1404,4320,12960,39204,117612, 353808,1061424,3187188,9561564,28693440,86080320, 258267204,774801612,2324483568,6973450704, 20920588308,62761764924,188286003360,564858010080, 1694576156004] |