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A081398
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Number of common prime factors of sigma[n] and phi[n] is exactly six(ignoring multiplicity).
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0
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2003639, 2179316, 2180057, 2382974, 2689561, 2720567, 2761873, 2933675, 3145572, 3435381, 4007278, 4137111, 4212692, 4360114, 4947971, 5172881, 5379122, 5441134, 5458673
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| n=400:sigma[n]=6846840=2.2.2.3.3.5.7.11.13.19, phi[n]=1755600=2.2.2.2.3.5.5.7.11.19, common prime set={2,3,5,7,11,19} with six primes
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MATHEMATICA
| ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[ffi[x][[2*w - 1]], {w, 1, lf[x]}] Do[s=Length[Intersection[ba[EulerPhi[n]], ba[DivisorSigma[1, n]]]]; If[Greater[s, 5], than Print[{n, s}]], {n, 1, 10000000}]
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CROSSREFS
| Cf. A000010, A000203, A081383, A081397, A002110.
Sequence in context: A017589 A067454 A172791 * A022226 A032754 A104441
Adjacent sequences: A081395 A081396 A081397 * A081399 A081400 A081401
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Mar 28 2003
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