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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 21 |
| 4 | 568 |
| 5 | 539379 |
| 6 | 620246356844 |
| 7 | 692770666469748075583580 |
| 8 | 1025344764595988314871439935857378400856992018101 |
[1,2,5,21,568,539379,620246356844, 692770666469748075583580, 1025344764595988314871439935857378400856992018101] |