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A202534
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Number of symmetric, reflexive, non-transitive relations on n elements.
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0
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0, 0, 3, 49, 972, 32565, 2096275, 268431316, 68719455589, 35184371972857, 36028797018285398, 73786976294833992867, 302231454903657266032107, 2475880078570760549607349126, 40564819207303340847893119613487, 1329227995784915872903807049800202429
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OFFSET
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1,3
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COMMENTS
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Of the values shown, only 3 is prime. Are there any other prime values in the sequence? - Jonathan Vos Post, Dec 29 2011
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LINKS
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FORMULA
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EXAMPLE
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The first symmetric, reflexive, nontransitive relation occurs for n=3: omitting a non-identical couple (a,b) from the total relation gives such a relation (and for n=3, this is the only way). There are 3 ways to choose this couple.
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PROG
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(Sage) def a(n): return 2^(n*(n-1)/2) - bell_number(n)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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