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Numbers k such that phi(k+12) = phi(k) + 12.
1

%I #13 Mar 01 2020 04:41:33

%S 5,7,11,17,19,29,31,41,45,47,59,61,65,67,71,80,89,97,99,101,112,117,

%T 127,135,137,139,151,167,171,176,179,181,196,199,207,209,211,227,229,

%U 239,251,257,269,271,272,279,281,294,304,310,312,337,347,367,369,389

%N Numbers k such that phi(k+12) = phi(k) + 12.

%C Prime solutions are in A046133, common with primes in A015917.

%H Amiram Eldar, <a href="/A056775/b056775.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Harvey P. Dale)

%e 65 is a term since phi(65) = 48, phi(65+12) = phi(77) = 60 = 48 + 12.

%t Select[Range[400],EulerPhi[#]+12==EulerPhi[#+12]&] (* _Harvey P. Dale_, Jan 21 2013 *)

%Y Cf. A000010, A001838, A015917, A054902, A046133, A046133.

%K nonn

%O 1,1

%A _Labos Elemer_, Aug 17 2000