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Search: id:A081380
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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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+0
2
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| 1, 180, 1444, 12996, 23805, 36100, 52020, 60228, 64980, 68832, 95220, 301140, 324900, 344160, 481824
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OFFSET
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1,2
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REFERENCES
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J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 180, p. 56, Ellipses, Paris 2008.
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EXAMPLE
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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
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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]}] 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
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Cf. A000203, A001157, A081377-A081379.
Adjacent sequences: A081377 A081378 A081379 this_sequence A081381 A081382 A081383
Sequence in context: A143793 A032774 A032776 this_sequence A115184 A099106 A112068
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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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EXTENSIONS
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More terms from Lekraj Beedassy (blekraj(AT)yahoo.com), Jul 18 2008
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