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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 20 |
| 3 | 155 |
| 4 | 1220 |
| 5 | 10630 |
| 6 | 98900 |
| 7 | 960650 |
| 8 | 9613700 |
| 9 | 98462675 |
| 10 | 1027222520 |
| 11 | 10877596900 |
| 12 | 116613287300 |
| 13 | 1263159501180 |
| 14 | 13803839298920 |
| 15 | 152000845788280 |
| 16 | 1684888825463940 |
| 17 | 18785707522181965 |
| 18 | 210536007879090140 |
| 19 | 2370423142929112065 |
| 20 | 26799168520704093720 |
[1,5,20,155,1220,10630,98900,960650,9613700, 98462675,1027222520,10877596900,116613287300, 1263159501180,13803839298920,152000845788280, 1684888825463940,18785707522181965, 210536007879090140,2370423142929112065, 26799168520704093720] |