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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 252 |
| 3 | 2275 |
| 4 | 17052 |
| 5 | 111594 |
| 6 | 657419 |
| 7 | 3557256 |
| 8 | 17931459 |
| 9 | 85093393 |
| 10 | 383211885 |
| 11 | 1648114587 |
| 12 | 6803773998 |
| 13 | 27073141326 |
| 14 | 104199172863 |
| 15 | 389047640905 |
| 16 | 1412682672765 |
| 17 | 4999550830281 |
| 18 | 17277525329491 |
| 19 | 58400376126855 |
| 20 | 193361098926450 |
| 21 | 627924447630011 |
| 22 | 2002332877504113 |
[1,21,252,2275,17052,111594,657419,3557256, 17931459,85093393,383211885,1648114587,6803773998, 27073141326,104199172863,389047640905, 1412682672765,4999550830281,17277525329491, 58400376126855,193361098926450,627924447630011, 2002332877504113] |