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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 90 |
| 5 | 692 |
| 6 | 5774 |
| 7 | 48924 |
| 8 | 417440 |
| 9 | 3580036 |
| 10 | 30831756 |
| 11 | 266463804 |
| 12 | 2309848194 |
| 13 | 20074999500 |
| 14 | 174867895438 |
| 15 | 1526259877412 |
| 16 | 13344806416950 |
| 17 | 116863477094660 |
| 18 | 1024844657752730 |
| 19 | 8998915251701628 |
| 20 | 79108591391227406 |
| 21 | 696167664755023388 |
| 22 | 6132277201334483178 |
[1,2,6,20,90,692,5774,48924,417440,3580036, 30831756,266463804,2309848194,20074999500, 174867895438,1526259877412,13344806416950, 116863477094660,1024844657752730,8998915251701628, 79108591391227406,696167664755023388, 6132277201334483178] |