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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 22 |
| 3 | 172 |
| 4 | 1513 |
| 5 | 14356 |
| 6 | 143228 |
| 7 | 1480956 |
| 8 | 15728516 |
| 9 | 170558634 |
| 10 | 1880568650 |
| 11 | 21019304814 |
| 12 | 237615558790 |
| 13 | 2712066792304 |
| 14 | 31210387143556 |
| 15 | 361738488066632 |
| 16 | 4218907281330372 |
| 17 | 49476183230651216 |
| 18 | 583066018329260673 |
| 19 | 6901459436855306662 |
| 20 | 82011678696864842013 |
[1,4,22,172,1513,14356,143228,1480956,15728516, 170558634,1880568650,21019304814,237615558790, 2712066792304,31210387143556,361738488066632, 4218907281330372,49476183230651216, 583066018329260673,6901459436855306662, 82011678696864842013] |