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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 51 |
| 4 | 470 |
| 5 | 4716 |
| 6 | 49350 |
| 7 | 534115 |
| 8 | 5929892 |
| 9 | 67175779 |
| 10 | 773473709 |
| 11 | 9025907984 |
| 12 | 106511693025 |
| 13 | 1268898400188 |
| 14 | 15240421643846 |
| 15 | 184348620664449 |
| 16 | 2243749948233175 |
| 17 | 27459089491691552 |
| 18 | 337685454820968084 |
| 19 | 4170918486201555250 |
| 20 | 51719670553572755173 |
| 21 | 643610071084847351183 |
[1,1,6,51,470,4716,49350,534115,5929892,67175779, 773473709,9025907984,106511693025,1268898400188, 15240421643846,184348620664449,2243749948233175, 27459089491691552,337685454820968084, 4170918486201555250,51719670553572755173, 643610071084847351183] |