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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 68 |
| 5 | 720 |
| 6 | 9804 |
| 7 | 163184 |
| 8 | 3210192 |
| 9 | 72870120 |
| 10 | 1874721360 |
| 11 | 53905894152 |
| 12 | 1713195438624 |
| 13 | 59633476003920 |
| 14 | 2256257009704320 |
| 15 | 92196226214092800 |
| 16 | 4046446853549201664 |
| 17 | 189845257963376620800 |
| 18 | 9481546020840245199360 |
| 19 | 502242773970728703225600 |
| 20 | 28124368575613839072714240 |
[1,2,9,68,720,9804,163184,3210192,72870120, 1874721360,53905894152,1713195438624, 59633476003920,2256257009704320,92196226214092800, 4046446853549201664,189845257963376620800, 9481546020840245199360,502242773970728703225600, 28124368575613839072714240] |