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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 210 |
| 3 | 1386 |
| 4 | 6930 |
| 5 | 28314 |
| 6 | 99099 |
| 7 | 306735 |
| 8 | 858858 |
| 9 | 2212210 |
| 10 | 5309304 |
| 11 | 11992344 |
| 12 | 25697880 |
| 13 | 52581816 |
| 14 | 103285710 |
| 15 | 195635286 |
| 16 | 358664691 |
| 17 | 638489775 |
| 18 | 1106715610 |
| 19 | 1872263250 |
| 20 | 3097744650 |
| 21 | 5021809650 |
| 22 | 7989242625 |
| 23 | 12491007165 |
| 24 | 19216934100 |
| 25 | 29124331236 |
| 26 | 43526473056 |
[1,21,210,1386,6930,28314,99099,306735,858858, 2212210,5309304,11992344,25697880,52581816, 103285710,195635286,358664691,638489775, 1106715610,1872263250,3097744650,5021809650, 7989242625,12491007165,19216934100,29124331236, 43526473056] |