A132793 - OEIS

%I #16 Sep 08 2024 19:25:29

%S 3,70,138,792,924,1692,1932,2124,2250,2988,3852,30936,112644,189252,

%T 240120,261660,263928,338760,364308,379470,390432,504216,529110,

%U 785568,862290,917700,979596,1022310,1124220,1404270,1434072,2004372,2526000

%N Numbers n such that sigma(phi(n))-phi(n) = phi(sigma(n)-n).

%C Used sigma(n)-n, namely the sum of proper divisors.

%H Donovan Johnson, <a href="/A132793/b132793.txt">Table of n, a(n) for n = 1..100</a>

%p with(numtheory); P:=proc(n) local i,j,k; for i from 1 by 1 to n do j:=sigma(phi(i))-phi(i); k:=phi(sigma(i)-i); if j=k then print(i); fi; od; end: P(150000);

%t Select[Range[2600000],DivisorSigma[1,EulerPhi[#]]-EulerPhi[#]==EulerPhi[ DivisorSigma[1,#]-#]&] (* _Harvey P. Dale_, Mar 24 2016 *)

%o (PARI) isA132793(n)={ if( sigma(eulerphi(n))-eulerphi(n) == eulerphi(sigma(n)-n), 1, 0 ) ; }

%o { for(n=2,6000000, if(isA132793(n), print1(n, ", ") ; ) ; ) ; } \\ _R. J. Mathar_, Nov 11 2007

%Y Cf. A000010, A000203, A001229, A018784, A033632, A132794.

%K nonn

%O 1,1

%A _Paolo P. Lava_ and _Giorgio Balzarotti_, Aug 31 2007

%E More terms from _R. J. Mathar_, Nov 11 2007

%E Invalid first term removed by _Donovan Johnson_, Sep 11 2013