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A135470
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Composite numbers n that divide 2 * sigma(n) - d(n) [that is, 2 * sum of divisors - number of divisors].
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1
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18, 70, 88, 132, 780, 11096, 17816, 518656, 1713592, 9928792, 11547352, 13499120, 17999992, 89283592, 134094848, 173482552, 175519344, 318836720, 903230984, 1081850752, 2146926592, 16709332608, 18543186000, 34177937500
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OFFSET
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1,1
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COMMENTS
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It is conjectured that there are no odd terms and that the sequence is infinite.
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LINKS
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MATHEMATICA
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Select[Range[172*10^4], CompositeQ[#]&&Divisible[2*DivisorSigma[1, #]-DivisorSigma[ 0, #], #]&] (* The program generates the first 9 terms of the sequence. To generate more, increase the Range constant. *) (* Harvey P. Dale, May 11 2020 *)
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PROG
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(PARI) isok(n) = (! isprime(n) && (2*sigma(n) - numdiv(n)) % n == 0) \\ Michel Marcus, Jun 09 2013
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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