A070556 a(n) = cototient(totient(n)).

0, 0, 1, 1, 2, 1, 4, 2, 4, 2, 6, 2, 8, 4, 4, 4, 8, 4, 12, 4, 8, 6, 12, 4, 12, 8, 12, 8, 16, 4, 22, 8, 12, 8, 16, 8, 24, 12, 16, 8, 24, 8, 30, 12, 16, 12, 24, 8, 30, 12, 16, 16, 28, 12, 24, 16, 24, 16, 30, 8, 44, 22, 24, 16, 32, 12, 46, 16, 24, 16, 46, 16, 48

Offset: 1

Author

N. J. A. Sloane, May 06 2002

Keywords

• nonn
• look

Links

• G. C. Greubel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A051953, A054571.

Programs

Magma

[EulerPhi(n)-EulerPhi(EulerPhi(n)): n in [1..100]]; // Vincenzo Librandi, Aug 06 2015

Maple

A051953 := proc(n)
        n-numtheory[phi](n) ;
end proc:
A070556 := proc(n)
        A051953(numtheory[phi](n)) ;
end proc: # R. J. Mathar, Oct 13 2011

Mathematica

Table[EulerPhi[n] - EulerPhi[EulerPhi[n]], {n, 80}] (* Vincenzo Librandi, Aug 06 2015 *)

Formula

a(n) = A051953(A000010(n)).