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A179931
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a(n) = gcd(sigma(n), sigma_2(n)).
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7
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1, 1, 2, 7, 2, 2, 2, 5, 13, 2, 2, 14, 2, 2, 4, 31, 2, 13, 2, 42, 4, 2, 2, 10, 31, 2, 20, 14, 2, 4, 2, 21, 4, 2, 4, 91, 2, 10, 4, 10, 2, 4, 2, 42, 26, 2, 2, 62, 57, 93, 4, 14, 2, 20, 4, 10, 20, 10, 2, 84, 2, 2, 26, 127, 4, 4, 2, 42, 4, 4, 2, 65, 2, 2, 62, 14, 4, 4, 2, 62, 121, 2, 2, 28, 4, 2, 20, 10, 2, 26, 4, 42, 4, 2, 4, 42, 2, 57, 26, 217
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OFFSET
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1,3
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COMMENTS
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A006530(a(n)) = A082066(n). - Reinhard Zumkeller, Jul 10 2011, the latter A-number corrected by Antti Karttunen, May 22 2017.
Not multiplicative: a(2)*a(19) <> a(38). - R. J. Mathar, Oct 08 2011
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LINKS
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Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
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MAPLE
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A179931 := proc(n) igcd( numtheory[sigma](n), numtheory[sigma][2](n)) ; end proc:
seq(A179931(n), n=1..100) ;
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MATHEMATICA
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Table[GCD @@ Map[DivisorSigma[#, n] &, {1, 2}], {n, 100}] (* Michael De Vlieger, May 22 2017 *)
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PROG
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(PARI) a(n)=gcd(sigma(n), sigma(n, 2)) \\ Charles R Greathouse IV, Feb 14 2013
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CROSSREFS
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Cf. A179930, A000203, A001157, A082066, A009194.
Sequence in context: A195476 A082072 A082066 * A130335 A347236 A073246
Adjacent sequences: A179928 A179929 A179930 * A179932 A179933 A179934
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane, Jul 09 2011, following a suggestion from R. J. Mathar
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STATUS
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approved
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