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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 28 |
| 5 | 262 |
| 6 | 2944 |
| 7 | 37666 |
| 8 | 532276 |
| 9 | 8151322 |
| 10 | 133562194 |
| 11 | 2320621222 |
| 12 | 42475263136 |
| 13 | 814932467836 |
| 14 | 16326188799508 |
| 15 | 340479903535258 |
| 16 | 7373196169450312 |
| 17 | 165453350568966163 |
| 18 | 3840489521467649158 |
| 19 | 92072430090995120044 |
| 20 | 2276807696679096394552 |
[1,1,4,28,262,2944,37666,532276,8151322,133562194, 2320621222,42475263136,814932467836, 16326188799508,340479903535258,7373196169450312, 165453350568966163,3840489521467649158, 92072430090995120044,2276807696679096394552] |