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Search: id:A081379
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| A081379 |
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Both sums and sets of prime factors of sigma[n] and phi[n] - ignoring multiplicity are equal to each other. |
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3
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| 1, 3, 14, 35, 42, 70, 105, 119, 209, 210, 238, 248, 297, 357, 418, 477, 594, 595, 616, 627, 714, 744, 954, 1045, 1178, 1190, 1240, 1254, 1463, 1485, 1672, 1674, 1736, 1785, 1848, 1863, 2079, 2090, 2376, 2385, 2540, 2728, 2926, 2945, 2970
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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Intersection of A076533 and A081377.
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EXAMPLE
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n=477=3.3.53: sigma(477)=702=2.3.3.3.13,phi[477]=312=2.2.2.3.13, common factor-set:{2,3,13}, sum=18
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MATHEMATICA
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ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] spf[x_] := Apply[Plus, ba[x]] k=0; Do[s=ba[DivisorSigma[1, n]]; s1=ba[EulerPhi[n]]; s3=spf[DivisorSigma[1, n]]; s4=spf[EulerPhi[n]]; If[Equal[s, s1]&&Equal[s3, s4], k=k+1; Print[{n, s, s1, ba[n], s3}]], {n, 1, 10000}]
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CROSSREFS
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Cf. A000010, A000203, A076533, A065642, A081377, A081378.
Sequence in context: A094627 A009394 A076533 this_sequence A081377 A050934 A110427
Adjacent sequences: A081376 A081377 A081378 this_sequence A081380 A081381 A081382
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Mar 26 2003
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