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A015770
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Numbers k such that phi(k) divides sigma_12(k).
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10
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OFFSET
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1,2
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COMMENTS
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sigma_12(n) = A013960(n) is the sum of the 12th powers of the divisors of n.
sigma(24j+12,x)/phi(x) is an integer for j in the range 0, ..., 500 for x = 1, 2, 3, 6, 249, 498, 118578 and supposed to hold for possible larger terms of A015770 and all j. Compare with comments to A015759, A091285, A015762. - Labos Elemer, May 27 2004
All known terms of A015762 (and also of this sequence) are squarefree. In that case, sigma_12(x)/sigma_4(x) = Product_{primes p|x} (p^8 - p^4 + 1) is an integer, so x is also in this sequence. - M. F. Hasler, Aug 22 2017
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LINKS
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MATHEMATICA
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Select[Range[1200000], Divisible[DivisorSigma[12, #], EulerPhi[#]]&] (* Harvey P. Dale, Dec 04 2015 *)
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CROSSREFS
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Cf. A020492, A015759, A015761, A015762, A015763, A015764, A015765, A015766, A015767, A015768, A015769, A015771, A015773, A015774, A094470.
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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