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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 20 |
| 3 | 429 |
| 4 | 5920 |
| 5 | 63954 |
| 6 | 510927 |
| 7 | 3362288 |
| 8 | 17975676 |
| 9 | 83628636 |
| 10 | 335900991 |
| 11 | 1222011613 |
| 12 | 3989760008 |
| 13 | 12105111844 |
| 14 | 33802351881 |
| 15 | 89361617169 |
| 16 | 221117356432 |
| 17 | 524533042878 |
| 18 | 1178959072101 |
| 19 | 2564070846089 |
| 20 | 5330170938874 |
| 21 | 10795501502457 |
[0,20,429,5920,63954,510927,3362288,17975676, 83628636,335900991,1222011613,3989760008, 12105111844,33802351881,89361617169,221117356432, 524533042878,1178959072101,2564070846089, 5330170938874,10795501502457] |