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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 358 |
| 4 | 3740 |
| 5 | 40194 |
| 6 | 439998 |
| 7 | 4879326 |
| 8 | 54630316 |
| 9 | 616194700 |
| 10 | 6991215286 |
| 11 | 79700776588 |
| 12 | 912207989030 |
| 13 | 10475536585674 |
| 14 | 120641989237890 |
| 15 | 1392811194744288 |
| 16 | 16114668707519404 |
| 17 | 186798818992569818 |
| 18 | 2168990381036497812 |
| 19 | 25222834639587149890 |
| 20 | 293708687012053512870 |
[1,4,36,358,3740,40194,439998,4879326,54630316, 616194700,6991215286,79700776588,912207989030, 10475536585674,120641989237890,1392811194744288, 16114668707519404,186798818992569818, 2168990381036497812,25222834639587149890, 293708687012053512870] |