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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 136 |
| 3 | 650 |
| 4 | 2331 |
| 5 | 6860 |
| 6 | 17472 |
| 7 | 39852 |
| 8 | 83325 |
| 9 | 162382 |
| 10 | 298584 |
| 11 | 522886 |
| 12 | 878423 |
| 13 | 1423800 |
| 14 | 2236928 |
| 15 | 3419448 |
| 16 | 5101785 |
| 17 | 7448874 |
| 18 | 10666600 |
| 19 | 15008994 |
| 20 | 20786227 |
| 21 | 28373444 |
| 22 | 38220480 |
| 23 | 50862500 |
| 24 | 66931605 |
| 25 | 87169446 |
| 26 | 112440888 |
| 27 | 143748766 |
[1,18,136,650,2331,6860,17472,39852,83325,162382, 298584,522886,878423,1423800,2236928,3419448, 5101785,7448874,10666600,15008994,20786227, 28373444,38220480,50862500,66931605,87169446, 112440888,143748766] |