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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 40 |
| 5 | 215 |
| 6 | 1446 |
| 7 | 11893 |
| 8 | 115844 |
| 9 | 1302099 |
| 10 | 16568290 |
| 11 | 235237937 |
| 12 | 3684998208 |
| 13 | 63113398543 |
| 14 | 1173013230494 |
| 15 | 23509415868141 |
| 16 | 505358483764732 |
| 17 | 11597234229683147 |
| 18 | 282970077651917658 |
| 19 | 7314780938223880105 |
[0,0,2,9,40,215,1446,11893,115844,1302099, 16568290,235237937,3684998208,63113398543, 1173013230494,23509415868141,505358483764732, 11597234229683147,282970077651917658, 7314780938223880105] |