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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 123 |
| 5 | 823 |
| 6 | 5878 |
| 7 | 44091 |
| 8 | 342935 |
| 9 | 2743484 |
| 10 | 224466889 |
| 11 | 18705574106 |
| 12 | 1582779347450 |
| 13 | 135666801210013 |
| 14 | 11757789438201155 |
| 15 | 1028806575842601095 |
| 16 | 90777050809641273099 |
| 17 | 8069071183079224275500 |
| 18 | 721969526907088487807963 |
[1,4,20,123,823,5878,44091,342935,2743484, 224466889,18705574106,1582779347450, 135666801210013,11757789438201155, 1028806575842601095,90777050809641273099, 8069071183079224275500,721969526907088487807963] |