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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 356 |
| 3 | 6096 |
| 4 | 102436 |
| 5 | 1702480 |
| 6 | 28093456 |
| 7 | 461273920 |
| 8 | 7546019620 |
| 9 | 123100218320 |
| 10 | 2003738272656 |
| 11 | 32557446669120 |
| 12 | 528231606378256 |
| 13 | 8559878182412096 |
| 14 | 138567392514153536 |
| 15 | 2241139725237406976 |
| 16 | 36219533239041063716 |
| 17 | 584958249814679707856 |
| 18 | 9441690077748181415696 |
[1,20,356,6096,102436,1702480,28093456,461273920, 7546019620,123100218320,2003738272656, 32557446669120,528231606378256,8559878182412096, 138567392514153536,2241139725237406976, 36219533239041063716,584958249814679707856, 9441690077748181415696] |