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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 12 |
| 5 | 57 |
| 6 | 321 |
| 7 | 2176 |
| 8 | 17008 |
| 9 | 150505 |
| 10 | 1485465 |
| 11 | 16170036 |
| 12 | 192384876 |
| 13 | 2483177809 |
| 14 | 34554278857 |
| 15 | 515620794592 |
| 16 | 8212685046336 |
| 17 | 139062777326001 |
| 18 | 2494364438359953 |
| 19 | 47245095998005060 |
| 20 | 942259727190907180 |
| 21 | 19737566982241851721 |
| 22 | 433234326593362631601 |
[1,1,4,12,57,321,2176,17008,150505,1485465, 16170036,192384876,2483177809,34554278857, 515620794592,8212685046336,139062777326001, 2494364438359953,47245095998005060, 942259727190907180,19737566982241851721, 433234326593362631601] |