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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 141 |
| 4 | 1125 |
| 5 | 9261 |
| 6 | 78255 |
| 7 | 673137 |
| 8 | 5864238 |
| 9 | 51592770 |
| 10 | 457484382 |
| 11 | 4082618376 |
| 12 | 36627119109 |
| 13 | 330070717935 |
| 14 | 2985857903655 |
| 15 | 27099681108948 |
| 16 | 246666402397287 |
| 17 | 2250904657271427 |
| 18 | 20586440729350197 |
| 19 | 188659279149885810 |
| 20 | 1732045683183434379 |
[1,3,18,141,1125,9261,78255,673137,5864238, 51592770,457484382,4082618376,36627119109, 330070717935,2985857903655,27099681108948, 246666402397287,2250904657271427, 20586440729350197,188659279149885810, 1732045683183434379] |