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A351540
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Numbers k that have an odd prime factor p such that p^(1+valuation(k,p)) divides sigma(k).
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2
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30, 51, 66, 96, 102, 120, 138, 159, 165, 174, 204, 210, 213, 246, 255, 264, 267, 282, 294, 306, 318, 321, 330, 345, 354, 357, 364, 390, 408, 426, 435, 462, 477, 480, 498, 510, 534, 537, 552, 561, 570, 591, 606, 615, 636, 642, 660, 663, 672, 678, 679, 690, 696, 699, 705, 714, 735, 745, 750, 753, 759, 760, 765, 786
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OFFSET
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1,1
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LINKS
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EXAMPLE
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30 = 2 * 3 * 5 is present as sigma(30) = 72 = 2^3 * 3^2, and thus there is at least one odd prime factor (in this case 3) such that a higher power of the same prime divides the sum of divisors of the same number.
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MATHEMATICA
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Select[Range[2, 800], Function[{k, s}, AnyTrue[DeleteCases[FactorInteger[k][[All, 1]], 2], Mod[s, #^(1 + IntegerExponent[k, #])] == 0 &]] @@ {#, DivisorSigma[1, #]} &] (* Michael De Vlieger, Feb 16 2022 *)
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PROG
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(PARI)
A351539(n) = { my(f=factor(n), s=sigma(n)); sum(k=1, #f~, (f[k, 1]%2)&&(0==(s%(f[k, 1]^(1+f[k, 2]))))); };
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CROSSREFS
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Positions of nonzero terms in A351539.
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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