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A081380
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Numbers n such that sets of prime factors(ignoring multiplicity) of A000203[n]=sigma[1,n] and of A001157[n]=sigma[2,n] are identical.
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1
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1, 180, 1444, 12996, 23805, 36100, 52020, 60228, 64980, 68832, 95220, 301140, 324900, 344160, 481824, 1505700, 1718721, 1720800, 2275758, 2409120, 3755844, 6874884, 6879645, 7965153, 8593605, 11378790, 12045600, 15930306, 17405892
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 180, p. 56, Ellipses, Paris 2008.
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EXAMPLE
| n=1444=2.2.19.19, sigma[1,1444]=2667=3.7.127, sigma[2,1444]=2744343=3.3.7.7.7.7.127, common factor-set={3,7,127}.
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MATHEMATICA
| ffi[x_] := Flatten[FactorInteger[x]] lf[x_] := Length[FactorInteger[x]] ba[x_] := Table[Part[ffi[x], 2*w-1], {w, 1, lf[x]}] Do[s=ba[DivisorSigma[1, n]]; s5=ba[DivisorSigma[2, n]]; If[Equal[s, s5], Print[n]], {n, 1, 1000000}]
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CROSSREFS
| Cf. A000203, A001157, A081377-A081379.
Sequence in context: A205818 A032774 A032776 * A115184 A154672 A184225
Adjacent sequences: A081377 A081378 A081379 * A081381 A081382 A081383
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Mar 26 2003
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EXTENSIONS
| More terms from Lekraj Beedassy (blekraj(AT)yahoo.com), Jul 18 2008
a(16)-a(29) from Donovan Johnson (donovan.johnson(AT)yahoo.com), May 24 2009
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