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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 33 |
| 5 | 220 |
| 6 | 1905 |
| 7 | 19250 |
| 8 | 220353 |
| 9 | 2820024 |
| 10 | 40211745 |
| 11 | 630374558 |
| 12 | 10781914209 |
| 13 | 199647892756 |
| 14 | 3981913796497 |
| 15 | 85074801848010 |
| 16 | 1938930641416577 |
| 17 | 46947275907107184 |
| 18 | 1203626305882706241 |
[1,0,1,6,33,220,1905,19250,220353,2820024, 40211745,630374558,10781914209,199647892756, 3981913796497,85074801848010,1938930641416577, 46947275907107184,1203626305882706241] |