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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 7 |
| 4 | 53 |
| 5 | 439 |
| 6 | 4121 |
| 7 | 43675 |
| 8 | 519249 |
| 9 | 6867463 |
| 10 | 100228877 |
| 11 | 1602238783 |
| 12 | 27866817297 |
| 13 | 524175098299 |
| 14 | 10606844137009 |
| 15 | 229807953097903 |
| 16 | 5308671596791901 |
| 17 | 130261745042452855 |
| 18 | 3383732450013895721 |
| 19 | 92770140175473602755 |
| 20 | 2677110186541556215233 |
[0,0,1,7,53,439,4121,43675,519249,6867463, 100228877,1602238783,27866817297,524175098299, 10606844137009,229807953097903,5308671596791901, 130261745042452855,3383732450013895721, 92770140175473602755,2677110186541556215233] |