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A179189
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Numbers n such that phi(n) = phi(n+7), with Euler's totient function phi = A000010.
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7
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5, 7, 21, 45, 75, 105, 285, 488, 585, 765, 1148, 1275, 1358, 1785, 2528, 3465, 4088, 6825, 9405, 12375, 14348, 15345, 16208, 16988, 23648, 25905, 25935, 42698, 50018, 52845, 54615, 61448, 62865, 68445, 78195, 80025, 82005, 88328, 93555, 98475
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OFFSET
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1,1
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COMMENTS
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There are 40 terms below 10^5, 81 terms below 10^6 and 162 terms below 10^7. There are 6606 terms below 10^12. [Jud McCranie, Feb 13 2012]
For n < 10^13, the only n such that phi(n-7) = phi(n) = phi(n+7) is 30057431145. - Giovanni Resta, Feb 27 2014
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range[100000], EulerPhi[#] == EulerPhi[# + 7] &] (* Vincenzo Librandi, Sep 08 2016 *)
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PROG
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(PARI) {op=vector(N=7); for( n=1, 1e5, if( op[n%N+1]+0==op[n%N+1]=eulerphi(n), print1(n-N, ", ")))}
(Magma) [n: n in [1..100000] | EulerPhi(n) eq EulerPhi(n+7)]; // Vincenzo Librandi, Sep 08 2016
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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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