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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 9 |
| 2 | 21 |
| 3 | 127 |
| 4 | 637 |
| 5 | 4007 |
| 6 | 24821 |
| 7 | 164659 |
| 8 | 1106197 |
| 9 | 7642295 |
| 10 | 53521277 |
| 11 | 380565539 |
| 12 | 2735155565 |
| 13 | 19854481655 |
| 14 | 145295269157 |
| 15 | 1070969265539 |
| 16 | 7943300521541 |
| 17 | 59241248227575 |
| 18 | 443987081678157 |
| 19 | 3342101935397795 |
| 20 | 25256877059336861 |
[1,9,21,127,637,4007,24821,164659,1106197,7642295, 53521277,380565539,2735155565,19854481655, 145295269157,1070969265539,7943300521541, 59241248227575,443987081678157,3342101935397795, 25256877059336861] |