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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 12 |
| 4 | 60 |
| 5 | 300 |
| 6 | 2100 |
| 7 | 14700 |
| 8 | 161700 |
| 9 | 1778700 |
| 10 | 19565700 |
| 11 | 215222700 |
| 12 | 2797895100 |
| 13 | 36372636300 |
| 14 | 618334817100 |
| 15 | 10511691890700 |
| 16 | 178698762141900 |
| 17 | 3037878956412300 |
| 18 | 57719700171833700 |
| 19 | 1096674303264840300 |
| 20 | 25223508975091326900 |
| 21 | 580140706427100518700 |
| 22 | 13343236247823311930100 |
[2,4,12,60,300,2100,14700,161700,1778700,19565700, 215222700,2797895100,36372636300,618334817100, 10511691890700,178698762141900,3037878956412300, 57719700171833700,1096674303264840300, 25223508975091326900,580140706427100518700, 13343236247823311930100] |