A054571 a(n) = phi(n - phi(n)), a(1) = 0.

0, 1, 1, 1, 1, 2, 1, 2, 2, 2, 1, 4, 1, 4, 6, 4, 1, 4, 1, 4, 6, 4, 1, 8, 4, 6, 6, 8, 1, 10, 1, 8, 12, 6, 10, 8, 1, 8, 8, 8, 1, 8, 1, 8, 12, 8, 1, 16, 6, 8, 18, 12, 1, 12, 8, 16, 12, 8, 1, 20, 1, 16, 18, 16, 16, 22, 1, 12, 20, 22, 1, 16, 1, 18, 24, 16, 16, 18, 1, 16, 18

Offset: 1

Author

J. Sandor (mstaicu(AT)dualnet.ro), Mar 09 2002

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A051953, A070556, A290087.

Programs

Maple

A051953 := proc(n)
        n-numtheory[phi](n) ;
end proc:
A054571 := proc(n)
        numtheory[phi](A051953(n)) ;
end proc: # R. J. Mathar, Oct 13 2011

Mathematica

Array[EulerPhi[# - EulerPhi@ #] &, 81] (* Michael De Vlieger, Aug 07 2017 *)

PARI

A054571(n) = if(1==n,0,eulerphi(n - eulerphi(n))); \\ Antti Karttunen, Aug 07 2017

Formula

a(1) = 0, and for n > 1, a(n) = totient(cototient(n)) = A000010(A051953(n)). - Antti Karttunen, Aug 07 2017

Extensions

Description clarified with a(1) = 0 explicitly set by convention. - Antti Karttunen, Aug 07 2017