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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 6 |
| 3 | 17 |
| 4 | 30 |
| 5 | 177 |
| 6 | 417 |
| 7 | 1857 |
| 8 | 4302 |
| 9 | 19457 |
| 10 | 47731 |
| 11 | 203777 |
| 12 | 509769 |
| 13 | 2134017 |
| 14 | 5462701 |
| 15 | 22347777 |
| 16 | 58104062 |
| 17 | 234029057 |
| 18 | 616919457 |
| 19 | 2450784257 |
| 20 | 6533317815 |
| 21 | 25664946177 |
| 22 | 69085604341 |
| 23 | 268766806017 |
| 24 | 729558799305 |
| 25 | 2814562533377 |
[0,2,6,17,30,177,417,1857,4302,19457,47731,203777, 509769,2134017,5462701,22347777,58104062, 234029057,616919457,2450784257,6533317815, 25664946177,69085604341,268766806017,729558799305, 2814562533377] |