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A070037
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Nonprime numbers k such that sigma(k) == k+1 (mod phi(k)).
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5
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OFFSET
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1,2
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COMMENTS
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Nonprime numbers k such that Chowla(k)/phi(k) is an integer.
3^30*13*852977547249259 and 3^36*13*621820631944710643 are also terms. - Giovanni Resta, Nov 14 2019
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LINKS
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EXAMPLE
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Below 30000000 only 5 composite numbers were found: C = {4,15,900,902,28611063}, Chowla(C) = {2,8,1920,504,17600976}, phi(C) = {2,8,240,504,17600976}, quotient = {1,1,8,1,1}.
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MATHEMATICA
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s2[x_] := DivisorSigma[1, x]-x-1 e0[x_] := EulerPhi[x] Do[s=s2[n]/e0[n]; If[IntegerQ[s]&&!PrimeQ[n], Print[{n, s2[n], e0[n], s}]], {n, 1, 1000000}]
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PROG
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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STATUS
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approved
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