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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 52 |
| 5 | 520 |
| 6 | 6666 |
| 7 | 102942 |
| 8 | 1864136 |
| 9 | 38742048 |
| 10 | 909090910 |
| 11 | 23775972550 |
| 12 | 685853880636 |
| 13 | 21633936185160 |
| 14 | 740800455037202 |
| 15 | 27368368148803710 |
| 16 | 1085102592571150096 |
| 17 | 45957792327018709120 |
| 18 | 2070863582910344082918 |
| 19 | 98920982783015679456198 |
| 20 | 4993219047619047619047620 |
[0,2,6,52,520,6666,102942,1864136,38742048, 909090910,23775972550,685853880636,21633936185160, 740800455037202,27368368148803710, 1085102592571150096,45957792327018709120, 2070863582910344082918,98920982783015679456198, 4993219047619047619047620] |