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A216782
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Numbers such that numerator(sigma(n)/n) is even and denominator(sigma(n)/n) is odd.
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7
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3, 5, 6, 7, 11, 13, 14, 15, 17, 19, 21, 22, 23, 27, 28, 29, 30, 31, 33, 35, 37, 38, 39, 41, 42, 43, 45, 46, 47, 51, 53, 54, 55, 57, 59, 60, 61, 62, 63, 65, 66, 67, 69, 70, 71, 73, 75, 77, 78, 79, 83, 84, 85, 86, 87, 89, 91, 92, 93, 94, 95, 97, 99, 101, 102
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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sigma(3)/3 = 4/3 (even/odd).
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MATHEMATICA
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Select[Range[1000], EvenQ[Numerator[DivisorSigma[1, #] / # ]] && OddQ[Denominator[DivisorSigma[1, #]/#]]&] (* Vincenzo Librandi, Jun 24 2014 *)
nedoQ[n_]:=Module[{ds=DivisorSigma[1, n]/n}, EvenQ[Numerator[ds]]&&OddQ[ Denominator[ ds]]]; Select[Range[200], nedoQ] (* Harvey P. Dale, Feb 28 2015 *)
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PROG
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(PARI) eoab(n) = {for (i=1, n, ab = sigma(i)/i; if ((numerator(ab) % 2 == 0) && (denominator(ab) % 2 == 1), print1(i, ", ")); ); }
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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