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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 53 |
| 5 | 455 |
| 6 | 2218 |
| 7 | 9702 |
| 8 | 59956 |
| 9 | 444998 |
| 10 | 2915881 |
| 11 | 16984838 |
| 12 | 100144150 |
| 13 | 638465320 |
| 14 | 4169033187 |
| 15 | 26450244798 |
| 16 | 164385366814 |
| 17 | 1031338919194 |
| 18 | 6581317747223 |
| 19 | 42129509368387 |
| 20 | 268046060285802 |
| 21 | 1701181410512570 |
[1,1,2,53,455,2218,9702,59956,444998,2915881, 16984838,100144150,638465320,4169033187, 26450244798,164385366814,1031338919194, 6581317747223,42129509368387,268046060285802, 1701181410512570] |