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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 151 |
| 4 | 1440 |
| 5 | 14835 |
| 6 | 160793 |
| 7 | 1806849 |
| 8 | 20859129 |
| 9 | 245905348 |
| 10 | 2947869600 |
| 11 | 35825319390 |
| 12 | 440372147956 |
| 13 | 5465555197818 |
| 14 | 68396554601013 |
| 15 | 862066323857486 |
| 16 | 10933638171672105 |
| 17 | 139439595024315675 |
| 18 | 1787056241039876890 |
| 19 | 23003636498360053905 |
| 20 | 297283046361025602900 |
[1,3,18,151,1440,14835,160793,1806849,20859129, 245905348,2947869600,35825319390,440372147956, 5465555197818,68396554601013,862066323857486, 10933638171672105,139439595024315675, 1787056241039876890,23003636498360053905, 297283046361025602900] |