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EXAMPLE
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Triangle begins:
[1] 1;
[2] 1, 2, 1;
[3] 1, 4, 9, 10, 6, 3, 1;
[4] 1, 7, 29, 87, 181, 287, 364, 365, 290, 187, 97, 39, 13, 4, 1;
...
There are 9 3-covers of an unlabeled 3-set: {{1,2},{2,3},{1,2,3}}, {{1,2},{2,3},{1,3}}, {{1,2},{3},{1,2,3}}, {{1},{1,2},{1,2,3}}, {{1,2},{2,3},{3}}, {{1,2},{2},{2,3}}, {{1},{2},{1,2,3}}, {{1},{2},{1,3}} and {{1},{2},{3}}.
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