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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 706 |
| 7 | 4844 |
| 8 | 37968 |
| 9 | 334656 |
| 10 | 3278896 |
| 11 | 35330098 |
| 12 | 415289184 |
| 13 | 5288377848 |
| 14 | 72522052240 |
| 15 | 1065579141202 |
| 16 | 16700472769061 |
| 17 | 278099720959114 |
| 18 | 4903387952699182 |
| 19 | 91258390273541562 |
| 20 | 1787828412527348984 |
| 21 | 36776310494510881628 |
| 22 | 792526608079806841508 |
[1,1,2,6,24,120,706,4844,37968,334656,3278896, 35330098,415289184,5288377848,72522052240, 1065579141202,16700472769061,278099720959114, 4903387952699182,91258390273541562, 1787828412527348984,36776310494510881628, 792526608079806841508] |