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A179187
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Numbers n such that phi(n)=phi(n+5), with Euler's totient function phi=A000010.
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10
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5, 9, 15, 21, 15556, 21016, 25930, 25935, 27027, 36304, 46683, 129675, 266128, 307923, 329175, 430348, 503139, 636400, 684411, 812170, 1014778, 1252713, 1777545, 1871788, 1892452, 1911987, 2622160, 2629930, 2731360, 2947035, 3397480, 4200100, 5451537
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OFFSET
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1,1
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COMMENTS
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There are only 43 terms below 10^7, and 1843 terms below 10^12. [Jud McCranie, Feb 13 2012]
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range[5000000], EulerPhi[#] == EulerPhi[# + 5] &] (* Vincenzo Librandi, Sep 08 2016 *)
Position[Partition[EulerPhi[Range[55*10^5]], 6, 1], _?(#[[1]] == #[[6]]&), {1}, Heads->False]//Flatten (* Harvey P. Dale, Nov 10 2016 *)
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PROG
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(PARI) {op=vector(N=5); for( n=1, 1e7, if( op[n%N+1]+0==op[n%N+1]=eulerphi(n), print1(n-N, ", ")))}
(Magma) [n: n in [1..5000000] | EulerPhi(n) eq EulerPhi(n+5)]; // 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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