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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 20 |
| 4 | 312 |
| 5 | 3573 |
| 6 | 31410 |
| 7 | 252630 |
| 8 | 1925590 |
| 9 | 14065552 |
| 10 | 99735307 |
| 11 | 691339079 |
| 12 | 4705890596 |
| 13 | 31562889402 |
| 14 | 209107683151 |
| 15 | 1370993621183 |
| 16 | 8908621893421 |
| 17 | 57438444240641 |
| 18 | 367809712917088 |
| 19 | 2341050421702590 |
| 20 | 14819986285211521 |
[0,1,20,312,3573,31410,252630,1925590,14065552, 99735307,691339079,4705890596,31562889402, 209107683151,1370993621183,8908621893421, 57438444240641,367809712917088,2341050421702590, 14819986285211521] |