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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 174 |
| 4 | 1231 |
| 5 | 8899 |
| 6 | 65492 |
| 7 | 487646 |
| 8 | 3664123 |
| 9 | 27723979 |
| 10 | 210946444 |
| 11 | 1612394958 |
| 12 | 12371547879 |
| 13 | 95230159650 |
| 14 | 735060394986 |
| 15 | 5687343753535 |
| 16 | 44096482961189 |
| 17 | 342530654187820 |
| 18 | 2665058975987628 |
| 19 | 20765913987073659 |
| 20 | 162019898098364055 |
| 21 | 1265622208055843635 |
[1,4,26,174,1231,8899,65492,487646,3664123, 27723979,210946444,1612394958,12371547879, 95230159650,735060394986,5687343753535, 44096482961189,342530654187820,2665058975987628, 20765913987073659,162019898098364055, 1265622208055843635] |