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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 21 |
| 3 | 56 |
| 4 | 231 |
| 5 | 888 |
| 6 | 4291 |
| 7 | 20646 |
| 8 | 107331 |
| 9 | 563786 |
| 10 | 3037314 |
| 11 | 16514106 |
| 12 | 90782986 |
| 13 | 502474356 |
| 14 | 2799220041 |
| 15 | 15673673176 |
| 16 | 88162676511 |
| 17 | 497847963696 |
| 18 | 2821127825971 |
| 19 | 16035812864946 |
| 20 | 91404068329560 |
[6,21,56,231,888,4291,20646,107331,563786,3037314, 16514106,90782986,502474356,2799220041, 15673673176,88162676511,497847963696, 2821127825971,16035812864946,91404068329560] |