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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 68 |
| 4 | 280 |
| 5 | 1168 |
| 6 | 4848 |
| 7 | 20160 |
| 8 | 83776 |
| 9 | 348224 |
| 10 | 1447296 |
| 11 | 6015488 |
| 12 | 25002240 |
| 13 | 103917568 |
| 14 | 431915008 |
| 15 | 1795179520 |
| 16 | 7461349376 |
| 17 | 31011794944 |
| 18 | 128895102976 |
| 19 | 535729963008 |
| 20 | 2226667929600 |
| 21 | 9254755975168 |
| 22 | 38465775239168 |
[1,4,16,68,280,1168,4848,20160,83776,348224, 1447296,6015488,25002240,103917568,431915008, 1795179520,7461349376,31011794944,128895102976, 535729963008,2226667929600,9254755975168, 38465775239168] |