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Search: id:A155609
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| 1, 2, 8, 38, 176, 782, 3368, 14198, 58976, 242462, 989528, 4017158, 16245776, 65514542, 263652488, 1059392918, 4251920576, 17050729022, 68332056248, 273715645478, 1096024843376, 4387586157902, 17560804984808, 70274600998838
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Let P(A) be the power set of an n-element set A and R be a relation on P(A) such that for all x, y of P(A), xRy if x and y are intersecting. Then a(n) = |R|. [From Ross La Haye (rlahaye(AT)new.rr.com), Mar 19 2009]
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REFERENCES
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Ross La Haye, Binary Relations on the Power Set of an n-Element Set, Journal of Integer Sequences, Vol. 12 (2009), Article 09.2.6. [From Ross La Haye (rlahaye(AT)new.rr.com), Mar 19 2009]
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FORMULA
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G.f.: 1/(1-4*x)-1/(1-3*x)+1/(1-x). E.g.f.: e^(4*x)-e^(3*x)+e^x.
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CROSSREFS
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A155596, A155597, A155598, A155599, A155600, A155601, A155602, A155603, A155604, A155605, A155606, A155607, A155608
Sequence in context: A159051 A053520 A112738 this_sequence A123164 A002003 A059423
Adjacent sequences: A155606 A155607 A155608 this_sequence A155610 A155611 A155612
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KEYWORD
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nonn
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AUTHOR
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Mohammad K. Azarian (azarian(AT)evansville.edu), Jan 26 2009
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