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A069235
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Numbers k, not perfect squares, such that the squarefree part of k divides sigma(k).
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3
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6, 24, 28, 40, 54, 96, 117, 120, 135, 147, 150, 216, 224, 234, 252, 270, 294, 360, 384, 468, 486, 496, 507, 540, 588, 600, 640, 672, 700, 726, 775, 819, 847, 864, 891, 931, 936, 1000, 1014, 1080, 1083, 1176, 1323, 1350, 1372, 1536, 1550, 1638, 1694, 1734
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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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54 is not a square, sigma(54)=120, 6 is the squarefree part of 54 and 6 divides 120. Hence a(5)=54 is in the sequence.
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MATHEMATICA
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f[p_, e_] := p^Mod[e, 2]; sqfp[n_] := Times @@ f @@@ FactorInteger[n]; Select[Range[2000], (s = sqfp[#]) > 1 && Divisible[DivisorSigma[1, #], s] &] (* Amiram Eldar, May 10 2022 *)
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PROG
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(PARI) c=0; for(n=2, 244783, if(issquare(n)==0, if(sigma(n)%core(n)==0, c++; write("b069235.txt", c " " n)))) /* Donovan Johnson, Aug 18 2013 */
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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