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A064400
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Number of ordered pairs a,b of elements in the dihedral group D_2n such that the subgroup generated by the pair a,b is the entire group D_2n.
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2
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3, 6, 18, 24, 60, 36, 126, 96, 162, 120, 330, 144, 468, 252, 360, 384, 816, 324, 1026, 480, 756, 660, 1518, 576, 1500, 936, 1458, 1008, 2436, 720, 2790, 1536, 1980, 1632, 2520, 1296, 3996, 2052, 2808, 1920, 4920, 1512, 5418, 2640, 3240, 3036, 6486, 2304, 6174, 3000, 4896, 3744, 8268
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 3 * A002618(n) = 3 * n * phi(n).
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MATHEMATICA
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Table[a=GroupElements[DihedralGroup[n]]; Count[Flatten[Table[Table[GroupOrder[PermutationGroup[{a[[i]], a[[j]]}]], {i, 1, 2*n}], {j, 1, 2*n}]], 2*n], {n, 1, 20}] (* Geoffrey Critzer, Apr 14 2013 *)
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PROG
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(PARI) a(n) = 3 * n * eulerphi(n); /* Joerg Arndt, Apr 14 2013 */
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Sep 28 2001
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EXTENSIONS
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STATUS
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approved
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