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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 31 |
| 5 | 293 |
| 6 | 3326 |
| 7 | 44189 |
| 8 | 673471 |
| 9 | 11588884 |
| 10 | 222304897 |
| 11 | 4704612119 |
| 12 | 108897613826 |
| 13 | 2737023412199 |
| 14 | 74236203425281 |
| 15 | 2161288643251828 |
| 16 | 67228358271588991 |
| 17 | 2225173863019549229 |
| 18 | 78087247031912850686 |
| 19 | 2896042595237791161749 |
| 20 | 113184512236563589997407 |
[1,0,1,4,31,293,3326,44189,673471,11588884, 222304897,4704612119,108897613826,2737023412199, 74236203425281,2161288643251828,67228358271588991, 2225173863019549229,78087247031912850686, 2896042595237791161749,113184512236563589997407] |