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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 20 |
| 3 | 52 |
| 4 | 208 |
| 5 | 704 |
| 6 | 2720 |
| 7 | 10952 |
| 8 | 45888 |
| 9 | 195516 |
| 10 | 852260 |
| 11 | 3760588 |
| 12 | 16656832 |
| 13 | 73584076 |
| 14 | 323148964 |
| 15 | 1409241264 |
| 16 | 6099051768 |
| 17 | 26171960056 |
| 18 | 111250573364 |
| 19 | 468230400620 |
| 20 | 1951667338228 |
| 21 | 8063089066756 |
| 22 | 33057662096520 |
| 23 | 134680763671240 |
[4,20,52,208,704,2720,10952,45888,195516,852260, 3760588,16656832,73584076,323148964,1409241264, 6099051768,26171960056,111250573364,468230400620, 1951667338228,8063089066756,33057662096520, 134680763671240] |