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A054571 a(n) = phi(n - phi(n)), a(1) = 0. 8
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

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

FORMULA

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

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 *)

PROG

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

CROSSREFS

Cf. A000010, A051953, A070556, A290087.

Sequence in context: A023645 A167865 A218654 * A126865 A104640 A193335

Adjacent sequences:  A054568 A054569 A054570 * A054572 A054573 A054574

KEYWORD

nonn

AUTHOR

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

EXTENSIONS

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

STATUS

approved

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Last modified November 21 22:40 EST 2019. Contains 329383 sequences. (Running on oeis4.)