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A324707
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Tri-unitary perfect numbers: numbers k such that tsigma(k) = 2k, where tsigma(k) is the sum of the tri-unitary divisors of k (A324706).
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7
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6, 60, 90, 36720, 47520, 8173440, 22276800, 126463680, 597542400, 4201148160, 287704872000, 1632485836800
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OFFSET
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1,1
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COMMENTS
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Also in the sequence is 21623407345626345971712000.
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LINKS
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EXAMPLE
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36720 is in the sequence since its sum of tri-unitary divisors is A324706(36720) = 73440 = 2 * 36720.
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MATHEMATICA
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f[p_, e_] := If[e == 3, (p^4-1)/(p-1), If[e==6, (p^8-1)/(p^2-1), p^e+1]]; tsigma[1]=1; tsigma[n_]:= Times @@ f @@@ FactorInteger[n]; Select[Range[50000], tsigma[#]==2# &]
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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