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A046685
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Numbers k such that the sum of cubes of divisors of k and the sum of 4th powers of divisors of k are relatively prime.
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7
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1, 2, 4, 8, 9, 18, 25, 100, 121, 225, 289, 484, 529, 841, 1089, 1156, 1681, 2116, 2209, 2601, 2809, 3364, 3481, 4761, 5041, 6724, 6889, 7225, 7569, 7921, 8836, 10201, 11236, 11449, 12769, 13225, 13924, 15129, 17161, 18769, 19881, 20164, 21025
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OFFSET
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1,2
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COMMENTS
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It can be shown that this is a subsequence of A028982.
The only terms that are not in A062503 are 2, 8 and 18.
No term is divisible by a term of A002476.
p^2 is a term for every p in A003627. (End)
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LINKS
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MAPLE
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N:= 10^6: # to get all terms <= N
sort(select(filter, [seq(t^2, t=1..isqrt(N)), seq(2*t^2, t=1..isqrt(N/2))])); # Robert Israel, Jul 09 2018
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MATHEMATICA
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Select[Range[25000], CoprimeQ[DivisorSigma[3, #], DivisorSigma[4, #]] &] (* Michael De Vlieger, Aug 10 2023 *)
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PROG
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(PARI) isok(n) = gcd(sigma(n, 3), sigma(n, 4)) == 1; \\ Michel Marcus, Sep 24 2019
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CROSSREFS
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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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