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A232538
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Numbers n such that (n(n+1)/2) modulo sigma(n) = n.
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2
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33, 136, 145, 261, 897, 1441, 2016, 2241, 2353, 3808, 4320, 7201, 17101, 26937, 30721, 32896, 46593, 70561, 148960, 151633, 169345, 174592, 208801, 400401, 578593, 712801, 803800, 1040401, 1103233, 1596673, 2265121, 2377089, 3330001, 4357153, 5953024, 5962321
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OFFSET
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1,1
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COMMENTS
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Also numbers n such that antisigma(n) modulo sigma(n) = n. Antisigma(n) = A024816(n) = the sum of the nondivisors of n that are between 1 and n, sigma(n) = A000203(n) = the sum of the divisors of n.
Numbers n such that A232324(n) = n.
a(19) > 10^5.
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LINKS
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FORMULA
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EXAMPLE
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136 is in sequence because antisigma(136) mod sigma(136) = 9046 mod 270 = 136.
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MATHEMATICA
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Select[Range[6*10^6], Mod[(#(#+1))/2, DivisorSigma[1, #]]==#&] (* Harvey P. Dale, Sep 12 2019 *)
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PROG
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(PARI) isok(n) = (n*(n+1)/2 - sigma(n)) % sigma(n) == n; \\ Michel Marcus, Nov 25 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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