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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 204 |
| 4 | 2255 |
| 5 | 30744 |
| 6 | 499121 |
| 7 | 9409960 |
| 8 | 202176360 |
| 9 | 4878316860 |
| 10 | 130651068911 |
| 11 | 3846719565780 |
| 12 | 123517560398401 |
| 13 | 4296240885694576 |
| 14 | 160935647131239840 |
| 15 | 6460088606857290384 |
| 16 | 276655979838719058119 |
| 17 | 12591439417867717440180 |
| 18 | 606947064800948702246681 |
[1,4,24,204,2255,30744,499121,9409960,202176360, 4878316860,130651068911,3846719565780, 123517560398401,4296240885694576, 160935647131239840,6460088606857290384, 276655979838719058119,12591439417867717440180, 606947064800948702246681] |