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| n | a(n) |
|---|---|
| 0 | 3 |
| 1 | 20 |
| 2 | 105 |
| 3 | 504 |
| 4 | 2310 |
| 5 | 10296 |
| 6 | 45045 |
| 7 | 194480 |
| 8 | 831402 |
| 9 | 3527160 |
| 10 | 14872858 |
| 11 | 62403600 |
| 12 | 260757900 |
| 13 | 1085822640 |
| 14 | 4508102925 |
| 15 | 18668849760 |
| 16 | 77138650050 |
| 17 | 318107374200 |
| 18 | 1309542023790 |
| 19 | 5382578744400 |
| 20 | 22093039119060 |
| 21 | 90567738003600 |
| 22 | 370847442355650 |
| 23 | 1516927277253024 |
[3,20,105,504,2310,10296,45045,194480,831402, 3527160,14872858,62403600,260757900,1085822640, 4508102925,18668849760,77138650050,318107374200, 1309542023790,5382578744400,22093039119060, 90567738003600,370847442355650,1516927277253024] |