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A082066
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Greatest common prime-divisor of sigma_1(n)=A000203(n) and sigma_2(n)=A001157(n); a(n)=1 if no common prime-divisor was found.
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3
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1, 1, 2, 7, 2, 2, 2, 5, 13, 2, 2, 7, 2, 2, 2, 31, 2, 13, 2, 7, 2, 2, 2, 5, 31, 2, 5, 7, 2, 2, 2, 7, 2, 2, 2, 13, 2, 5, 2, 5, 2, 2, 2, 7, 13, 2, 2, 31, 19, 31, 2, 7, 2, 5, 2, 5, 5, 5, 2, 7, 2, 2, 13, 127, 2, 2, 2, 7, 2, 2, 2, 13, 2, 2, 31, 7, 2, 2, 2, 31, 11, 2, 2, 7, 2, 2, 5, 5, 2, 13, 2, 7, 2, 2, 2, 7, 2
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OFFSET
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1,3
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LINKS
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Table of n, a(n) for n=1..97.
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FORMULA
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a(n) = A006530(A179931(n)). - Reinhard Zumkeller, Jul 10 2011
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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]}] f1[x_] := DivisorSigma[1, n]; f2[x_] := DivisorSigma[2, x] Table[Max[Intersection[ba[f1[w]], ba[f2[w]]]], {w, 1, 128}]
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PROG
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(PARI) gpf(n)=if(n>1, my(f=factor(n)[, 1]); f[#f], 1)
a(n)=gpf(gcd(sigma(n), sigma(n, 2))) \\ Charles R Greathouse IV, Feb 19 2013
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CROSSREFS
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Cf. A006530, A001157, A000203, A082061-A082065.
Sequence in context: A023399 A195476 A082072 * A179931 A130335 A073246
Adjacent sequences: A082063 A082064 A082065 * A082067 A082068 A082069
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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), Apr 07 2003
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STATUS
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approved
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