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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 1 |
| 4 | 21 |
| 5 | 168 |
| 6 | 1968 |
| 7 | 26094 |
| 8 | 398653 |
| 9 | 6872377 |
| 10 | 132050271 |
| 11 | 2798695656 |
| 12 | 64866063276 |
| 13 | 1632224748984 |
| 14 | 44316286165297 |
| 15 | 1291392786926821 |
| 16 | 40202651019430461 |
| 17 | 1331640833909877144 |
| 18 | 46762037794122159492 |
| 19 | 1735328399106396110310 |
| 20 | 67858430028772637693845 |
[0,1,1,21,168,1968,26094,398653,6872377,132050271, 2798695656,64866063276,1632224748984, 44316286165297,1291392786926821,40202651019430461, 1331640833909877144,46762037794122159492, 1735328399106396110310,67858430028772637693845] |