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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 162 |
| 5 | 1506 |
| 6 | 16950 |
| 7 | 224190 |
| 8 | 3408930 |
| 9 | 58596930 |
| 10 | 1123663590 |
| 11 | 23782729950 |
| 12 | 550718680050 |
| 13 | 13849716607650 |
| 14 | 375904338960150 |
| 15 | 10952237584237950 |
| 16 | 340947694234397250 |
| 17 | 11294123783425733250 |
| 18 | 396665528378000631750 |
[1,4,22,162,1506,16950,224190,3408930,58596930, 1123663590,23782729950,550718680050, 13849716607650,375904338960150,10952237584237950, 340947694234397250,11294123783425733250, 396665528378000631750] |