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Search: id:A094573
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| A094573 |
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Triangle T(n,k) giving number of (<=2)-covers of an n-set with k blocks. |
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+0
2
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| 1, 1, 1, 3, 1, 1, 12, 20, 7, 1, 39, 169, 186, 59, 3, 1, 120, 1160, 2755, 2243, 661, 55, 1, 363, 7381, 33270, 52060, 33604, 9167, 910, 15, 1, 1092, 45500, 367087, 988750, 1126874, 601262, 151726, 16401, 525, 1, 3279, 276529, 3873786, 17005149
(list; graph; listen)
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OFFSET
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0,4
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COMMENT
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Cover of a set is (<=2)-cover if every element of the set is covered with at most two blocks of the cover.
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FORMULA
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E.g.f.: exp(-x-x^2/2*(exp(y)-1))*Sum(exp(y*binomial(n+1, 2))*x^n/n!, n=0..infinity).
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EXAMPLE
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1; 1; 1,3,1; 1,12,20,7; 1,39,169,186,59,3; 1,120,1160,2755,2243,661,55; ...
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CROSSREFS
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Cf. A094574, A059443, A060052.
Sequence in context: A128592 A156584 A129619 this_sequence A055154 A015112 A156869
Adjacent sequences: A094570 A094571 A094572 this_sequence A094574 A094575 A094576
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KEYWORD
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nonn
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AUTHOR
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Goran Kilibarda, Vladeta Jovovic (vladeta(AT)eunet.rs), May 12 2004
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