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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 23 |
| 4 | 127 |
| 5 | 783 |
| 6 | 4655 |
| 7 | 28015 |
| 8 | 167919 |
| 9 | 1007855 |
| 10 | 6046447 |
| 11 | 36280047 |
| 12 | 217677551 |
| 13 | 1306070767 |
| 14 | 7836413679 |
| 15 | 47018503919 |
| 16 | 282110979823 |
| 17 | 1692665966319 |
| 18 | 10155995623151 |
| 19 | 60935974088431 |
| 20 | 365615843831535 |
| 21 | 2193695064387311 |
[0,1,3,23,127,783,4655,28015,167919,1007855, 6046447,36280047,217677551,1306070767,7836413679, 47018503919,282110979823,1692665966319, 10155995623151,60935974088431,365615843831535, 2193695064387311] |