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| n | a(n) |
|---|---|
| 0 | 3 |
| 1 | 3 |
| 2 | 6 |
| 3 | 18 |
| 4 | 75 |
| 5 | 376 |
| 6 | 2261 |
| 7 | 15833 |
| 8 | 126669 |
| 9 | 1140021 |
| 10 | 11400211 |
| 11 | 125402325 |
| 12 | 1504827907 |
| 13 | 19562762799 |
| 14 | 273878679186 |
| 15 | 4108180187796 |
| 16 | 65730883004743 |
| 17 | 1117425011080641 |
| 18 | 20113650199451545 |
| 19 | 382159353789579365 |
| 20 | 7643187075791587304 |
| 21 | 160506928591623333394 |
[3,3,6,18,75,376,2261,15833,126669,1140021, 11400211,125402325,1504827907,19562762799, 273878679186,4108180187796,65730883004743, 1117425011080641,20113650199451545, 382159353789579365,7643187075791587304, 160506928591623333394] |