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A134605
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Composite numbers such that the square root of the sum of squares of their prime factors (with multiplicity) is an integer.
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20
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16, 48, 81, 320, 351, 486, 512, 625, 1080, 1260, 1350, 1375, 1792, 1836, 2070, 2145, 2175, 2401, 2730, 2772, 3072, 3150, 3510, 4104, 4305, 4625, 4650, 4655, 4998, 5880, 6000, 6174, 6545, 7098, 7128, 7182, 7650, 7791, 7889, 7956, 9030, 9108, 9295, 9324
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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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a(2)=48 since 48=2*2*2*2*3 and sqrt(4*2^2+3^2)=sqrt(25)=5.
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MATHEMATICA
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srssQ[n_]:=IntegerQ[Sqrt[Total[Flatten[Table[#[[1]], #[[2]]]&/@ FactorInteger[ n]]^2]]]; Select[Range[10000], CompositeQ[#]&&srssQ[#]&] (* Harvey P. Dale, Jan 22 2019 *)
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PROG
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(PARI) is(n)=my(f=factor(n)); issquare(sum(i=1, #f~, f[i, 1]^2*f[i, 2])) && !isprime(n) && n>1 \\ Charles R Greathouse IV, Apr 29 2015
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CROSSREFS
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Cf. A001597, A025475, A134333, A134344, A134376, A134600, A134602, A134608, A134611, A134616, A134618, A134620.
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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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