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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 21 |
| 4 | 140 |
| 5 | 575 |
| 6 | 1785 |
| 7 | 4606 |
| 8 | 10416 |
| 9 | 21330 |
| 10 | 40425 |
| 11 | 71995 |
| 12 | 121836 |
| 13 | 197561 |
| 14 | 308945 |
| 15 | 468300 |
| 16 | 690880 |
| 17 | 995316 |
| 18 | 1404081 |
| 19 | 1943985 |
| 20 | 2646700 |
| 21 | 3549315 |
| 22 | 4694921 |
| 23 | 6133226 |
| 24 | 7921200 |
| 25 | 10123750 |
| 26 | 12814425 |
| 27 | 16076151 |
| 28 | 20001996 |
[0,1,21,140,575,1785,4606,10416,21330,40425,71995, 121836,197561,308945,468300,690880,995316,1404081, 1943985,2646700,3549315,4694921,6133226,7921200, 10123750,12814425,16076151,20001996] |