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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 21 |
| 3 | 108 |
| 4 | 492 |
| 5 | 2100 |
| 6 | 8604 |
| 7 | 34272 |
| 8 | 133728 |
| 9 | 513648 |
| 10 | 1948560 |
| 11 | 7318080 |
| 12 | 27256896 |
| 13 | 100815936 |
| 14 | 370684608 |
| 15 | 1355996160 |
| 16 | 4938304512 |
| 17 | 17914202880 |
| 18 | 64760732928 |
| 19 | 233390693376 |
| 20 | 838784916480 |
| 21 | 3006980379648 |
| 22 | 10755352869888 |
[0,3,21,108,492,2100,8604,34272,133728,513648, 1948560,7318080,27256896,100815936,370684608, 1355996160,4938304512,17914202880,64760732928, 233390693376,838784916480,3006980379648, 10755352869888] |