A132793 Numbers n such that sigma(phi(n))-phi(n) = phi(sigma(n)-n).

3, 70, 138, 792, 924, 1692, 1932, 2124, 2250, 2988, 3852, 30936, 112644, 189252, 240120, 261660, 263928, 338760, 364308, 379470, 390432, 504216, 529110, 785568, 862290, 917700, 979596, 1022310, 1124220, 1404270, 1434072, 2004372, 2526000

Offset: 1

Author

Paolo P. Lava and Giorgio Balzarotti, Aug 31 2007

Keywords

• nonn

Comments

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

Links

• Donovan Johnson, Table of n, a(n) for n = 1..100

Crossrefs

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

Programs

Maple

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);

Mathematica

Select[Range[2600000],DivisorSigma[1,EulerPhi[#]]-EulerPhi[#]==EulerPhi[ DivisorSigma[1,#]-#]&] (* Harvey P. Dale, Mar 24 2016 *)

PARI

isA132793(n)={ if( sigma(eulerphi(n))-eulerphi(n) == eulerphi(sigma(n)-n), 1, 0 ) ; }
{ for(n=2,6000000, if(isA132793(n), print1(n, ", ") ; ) ; ) ; } \\ R. J. Mathar, Nov 11 2007

Extensions

More terms from R. J. Mathar, Nov 11 2007

Invalid first term removed by Donovan Johnson, Sep 11 2013