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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 116 |
| 5 | 659 |
| 6 | 3802 |
| 7 | 22146 |
| 8 | 129838 |
| 9 | 764731 |
| 10 | 4519504 |
| 11 | 26778943 |
| 12 | 158989206 |
| 13 | 945437948 |
| 14 | 5629314106 |
| 15 | 33553133752 |
| 16 | 200164459648 |
| 17 | 1194964743750 |
| 18 | 7138188267650 |
| 19 | 42662447719844 |
| 20 | 255091414376360 |
| 21 | 1525848441256765 |
[1,4,21,116,659,3802,22146,129838,764731,4519504, 26778943,158989206,945437948,5629314106, 33553133752,200164459648,1194964743750, 7138188267650,42662447719844,255091414376360, 1525848441256765] |