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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 220 |
| 6 | 1590 |
| 7 | 12978 |
| 8 | 118664 |
| 9 | 1201464 |
| 10 | 13349610 |
| 11 | 161530270 |
| 12 | 2114578092 |
| 13 | 29780308116 |
| 14 | 448995414686 |
| 15 | 7215997736010 |
| 16 | 123153028027920 |
| 17 | 2224451568754288 |
| 18 | 42395429898611154 |
| 19 | 850263899633257014 |
| 20 | 17900292623858042420 |
| 21 | 394701452356069835340 |
| 22 | 9096928711444657157382 |
| 23 | 218739785834282892557026 |
[0,2,6,36,220,1590,12978,118664,1201464,13349610, 161530270,2114578092,29780308116,448995414686, 7215997736010,123153028027920,2224451568754288, 42395429898611154,850263899633257014, 17900292623858042420,394701452356069835340, 9096928711444657157382,218739785834282892557026] |