A063739 - OEIS

%I #22 Feb 26 2024 01:23:17

%S 1,3,15,194,255,2834,3255,3705,5186,5187,11715,22935,25545,49215,

%T 49335,65535,214334,256274,388245,525986,568815,589407,840255,936494,

%U 1259642,1574727,1659585,1759874,1788254,2123583,2200694,2521694,2619705,3240614,3289934

%N Squarefree numbers k such that phi(k) = phi(k+1).

%H Amiram Eldar, <a href="/A063739/b063739.txt">Table of n, a(n) for n = 1..3547</a> (terms below 10^13 calculated from the b-file at A001274; terms 1..75 from Harry J. Smith, terms 76..1000 from Donovan Johnson)

%t Select[Range[3000000],SquareFreeQ[#]&&EulerPhi[#]==EulerPhi[#+1]&] (* _Harvey P. Dale_, May 15 2013 *)

%o (PARI) for(n=1,10^7, if(issquarefree(n), if(eulerphi(n)==eulerphi(n+1),print(n))))

%o (PARI) { n=0; for (m=1, 10^9, if (eulerphi(m)==eulerphi(m + 1) && issquarefree(m), write("b063739.txt", n++, " ", m); if (n==75, break)) ) } \\ _Harry J. Smith_, Aug 29 2009

%Y Intersection of A005117 and A001274.

%K nonn

%O 1,2

%A _Jason Earls_, Aug 13 2001