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A067625
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Numbers n such that sigma(n) = phi(prime(n)+1).
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1
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23, 51, 77, 87, 114, 154, 158, 184, 210, 308, 552, 690, 786, 1330, 1848, 2030, 2280, 2868, 2976, 3432, 8680, 10290, 11556, 12750, 13110, 26400, 56808, 57960, 62496, 136290, 170478, 608580
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OFFSET
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1,1
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COMMENTS
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The sequence may be finite. Typically phi(prime(n)+1) will be on the order of n*log(n), while according to Grönwall's theorem sigma(n) = O(n * log log(n)). - Robert Israel, Sep 12 2014
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LINKS
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MAPLE
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MATHEMATICA
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Select[Range[610000], DivisorSigma[1, #]==EulerPhi[Prime[#]+1]&] (* Harvey P. Dale, Mar 17 2012 *)
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PROG
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(PARI) a067625(m) = for(n=1, m, if(sigma(n)==eulerphi(prime(n)+1), print1(n, ", ")))
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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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