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| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 10 |
| 2 | 60 |
| 3 | 455 |
| 4 | 3876 |
| 5 | 35420 |
| 6 | 339300 |
| 7 | 3362260 |
| 8 | 34179860 |
| 9 | 354465254 |
| 10 | 3735373880 |
| 11 | 39884521950 |
| 12 | 430571952300 |
| 13 | 4691735290080 |
| 14 | 51534335175776 |
| 15 | 570003171679020 |
| 16 | 6343110854237300 |
| 17 | 70968228417131850 |
| 18 | 797820661622862900 |
[4,10,60,455,3876,35420,339300,3362260,34179860, 354465254,3735373880,39884521950,430571952300, 4691735290080,51534335175776,570003171679020, 6343110854237300,70968228417131850, 797820661622862900] |