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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 142 |
| 5 | 1131 |
| 6 | 10422 |
| 7 | 112015 |
| 8 | 1396516 |
| 9 | 19702665 |
| 10 | 306547426 |
| 11 | 5177584809 |
| 12 | 94168757916 |
| 13 | 1833590759131 |
| 14 | 38009888806450 |
| 15 | 835064706091431 |
| 16 | 19389119390412448 |
| 17 | 475039405292487825 |
| 18 | 12263445905182200882 |
| 19 | 332913448508180564521 |
| 20 | 9478703390668813103836 |
[1,1,4,21,142,1131,10422,112015,1396516,19702665, 306547426,5177584809,94168757916,1833590759131, 38009888806450,835064706091431,19389119390412448, 475039405292487825,12263445905182200882, 332913448508180564521,9478703390668813103836] |