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A256937
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Numbers n such that phi(n) = 4*phi(n+1).
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4
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629, 1469, 85139, 100889, 139859, 154979, 168149, 304079, 396899, 838199, 1107413, 1323449, 1465463, 2088839, 2160899, 2504879, 2684879, 2693249, 2800181, 3404609, 3512249, 3576869, 3885881, 4241819, 4500509, 4620659, 4822649, 5530709, 5805449
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OFFSET
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1,1
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LINKS
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EXAMPLE
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phi(629) = 576 = 4*phi(630).
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MAPLE
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A:= NULL:
y:= numtheory:-phi(1):
for n from 1 to 10^6 do
x:= numtheory:-phi(n+1);
if y = 4*x then A:= A, n fi;
y:= x;
od:
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MATHEMATICA
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Select[Range@ 1000000, EulerPhi@ # == 4 EulerPhi[# + 1] &] (* Michael De Vlieger, Apr 13 2015 *)
Position[Partition[EulerPhi[Range[6*10^6]], 2, 1], _?(#[[1]]==4#[[2]]&), {1}, Heads->False]//Flatten (* Harvey P. Dale, Sep 18 2016 *)
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PROG
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(PARI) s=[]; for(n=1, 1000000, if(eulerphi(n)==4*eulerphi(n+1), s=concat(s, n))); s \\ Colin Barker, Apr 13 2015
(Magma) [n: n in [1..10^7] | EulerPhi(n) eq 4*EulerPhi(n+1)]; // Vincenzo Librandi, Apr 14 2015
(Sage) [n for n in (1..1000000) if euler_phi(n) == 4*euler_phi(n+1)]; # Bruno Berselli, Apr 14 2015
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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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