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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 19 |
| 5 | 144 |
| 6 | 1443 |
| 7 | 18295 |
| 8 | 280918 |
| 9 | 5069651 |
| 10 | 105147307 |
| 11 | 2464296222 |
| 12 | 64402891501 |
| 13 | 1856989724951 |
| 14 | 58560557062508 |
| 15 | 2004999890781363 |
| 16 | 74069439021212783 |
| 17 | 2936703201134924845 |
| 18 | 124383305232306494864 |
| 19 | 5605027085651919547476 |
| 20 | 267759074907470856179460 |
| 21 | 13516676464234372267564939 |
[1,1,1,4,19,144,1443,18295,280918,5069651, 105147307,2464296222,64402891501,1856989724951, 58560557062508,2004999890781363,74069439021212783, 2936703201134924845,124383305232306494864, 5605027085651919547476,267759074907470856179460, 13516676464234372267564939] |