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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 384 |
| 4 | 4568 |
| 5 | 57920 |
| 6 | 768760 |
| 7 | 10543120 |
| 8 | 148247390 |
| 9 | 2125715618 |
| 10 | 30965114225 |
| 11 | 456956616284 |
| 12 | 6817011617601 |
| 13 | 102640570550600 |
| 14 | 1557716916728198 |
| 15 | 23804070258610024 |
| 16 | 365964582592739540 |
| 17 | 5656501536118793076 |
| 18 | 87846324474413129008 |
| 19 | 1370097609728212588634 |
| 20 | 21451062781643458337802 |
[1,4,36,384,4568,57920,768760,10543120,148247390, 2125715618,30965114225,456956616284,6817011617601, 102640570550600,1557716916728198, 23804070258610024,365964582592739540, 5656501536118793076,87846324474413129008, 1370097609728212588634,21451062781643458337802] |