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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 20 |
| 3 | 220 |
| 4 | 1540 |
| 5 | 7770 |
| 6 | 30856 |
| 7 | 102340 |
| 8 | 295240 |
| 9 | 762355 |
| 10 | 1798940 |
| 11 | 3939936 |
| 12 | 8104460 |
| 13 | 15803060 |
| 14 | 29426320 |
| 15 | 52636760 |
| 16 | 90889616 |
| 17 | 152112005 |
| 18 | 247574180 |
| 19 | 392991060 |
| 20 | 609896980 |
| 21 | 927341646 |
| 22 | 1383960600 |
| 23 | 2030479100 |
| 24 | 2932714200 |
| 25 | 4175145975 |
| 26 | 5865135276 |
| 27 | 8137872120 |
[0,1,20,220,1540,7770,30856,102340,295240,762355, 1798940,3939936,8104460,15803060,29426320, 52636760,90889616,152112005,247574180,392991060, 609896980,927341646,1383960600,2030479100, 2932714200,4175145975,5865135276,8137872120] |