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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 18 |
| 5 | 166 |
| 6 | 2070 |
| 7 | 32505 |
| 8 | 614918 |
| 9 | 13600671 |
| 10 | 344202033 |
| 11 | 9806468970 |
| 12 | 310553772735 |
| 13 | 10820519947581 |
| 14 | 411338412455910 |
| 15 | 16940944600551504 |
| 16 | 751397442828052440 |
| 17 | 35707884976794347170 |
| 18 | 1810006747594245718317 |
[1,1,1,3,18,166,2070,32505,614918,13600671, 344202033,9806468970,310553772735,10820519947581, 411338412455910,16940944600551504, 751397442828052440,35707884976794347170, 1810006747594245718317] |