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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 24 |
| 5 | 216 |
| 6 | 2540 |
| 7 | 36930 |
| 8 | 639093 |
| 9 | 12821788 |
| 10 | 292495896 |
| 11 | 7475306400 |
| 12 | 211531253076 |
| 13 | 6564750305124 |
| 14 | 221684308001728 |
| 15 | 8091749562745576 |
| 16 | 317454163281499140 |
| 17 | 13320693233434444092 |
| 18 | 595287890670560958740 |
| 19 | 28226111104873887744528 |
| 20 | 1415312988632326542765024 |
[1,1,4,24,216,2540,36930,639093,12821788, 292495896,7475306400,211531253076,6564750305124, 221684308001728,8091749562745576, 317454163281499140,13320693233434444092, 595287890670560958740,28226111104873887744528, 1415312988632326542765024] |