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A087247
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Squarefree deficient nonprime numbers.
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5
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1, 10, 14, 15, 21, 22, 26, 33, 34, 35, 38, 39, 46, 51, 55, 57, 58, 62, 65, 69, 74, 77, 82, 85, 86, 87, 91, 93, 94, 95, 105, 106, 110, 111, 115, 118, 119, 122, 123, 129, 130, 133, 134, 141, 142, 143, 145, 146, 154, 155, 158, 159, 161, 165, 166, 170, 177, 178, 182, 183
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OFFSET
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1,2
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LINKS
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EXAMPLE
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105 = 3*5*7 and sigma(105) = 1 + 3 + 5 + 7 + 15 + 21 + 35 + 105 = 192 < 210 = 2*105, so 105 is in the sequence.
The sequence differs from A006881: first term with 3 distinct prime factors is 105.
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MATHEMATICA
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isA087247[n_] := SquareFreeQ[n] && !PrimeQ[n] && (DivisorSigma[1, n] < 2n); Select[Range[200], isA087247] (* Enrique Pérez Herrero, Jan 13 2011 *)
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PROG
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(PARI) isok(n) = !isprime(n) && issquarefree(n) && (sigma(n) < 2*n); \\ Michel Marcus, Jul 09 2018
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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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