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A053472 a(n) is the cototient of n (A051953) iterated 4 times. 4
0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 4, 0, 2, 0, 4, 0, 4, 0, 4, 0, 4, 0, 8, 0, 4, 1, 4, 0, 4, 0, 8, 0, 4, 0, 8, 0, 4, 1, 8, 0, 8, 0, 4, 1, 4, 0, 8, 0, 8, 0, 8, 0, 8, 0, 8, 0, 8, 0, 16, 0, 8, 1, 12, 0, 16, 1, 8, 0, 8, 0, 16, 0, 8, 0, 8, 0, 8, 0, 8, 1, 16, 0, 16 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,18

COMMENTS

As iteration of A051953 progresses, powers of 2 may appear and it ends at fixed point 0. Analogous 4th iterates for A000005 or A000010 are A036452 and A049100.

It is assumed here that the value of A051953 at 0 is 0. - Antti Karttunen, Dec 22 2017

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

EXAMPLE

n=50, n_1 = n - phi(n) = 50 - 20 = 30, n_2 = n_1 - Phi(n_1) = 30 - 8 = 22, n_3 = 22 - Phi(22) = 12, n_4 = n_3 - Phi(n_3) = 12 - 4 = 8 so the 50th term is 8.

MATHEMATICA

Array[Nest[# - EulerPhi@ # &, #, 4] &, 102] (* Michael De Vlieger, Dec 23 2017 *)

PROG

(PARI)

A051953(n) = if(!n, n, (n-eulerphi(n))); \\ With modification that returns zero for zero.

A053472(n) = A051953(A051953(A051953(A051953(n)))); \\ Antti Karttunen, Dec 22 2017

CROSSREFS

Cf. A051953, A000005, A000010, A036452, A049100.

Cf. A053470, A053471, A053473.

Sequence in context: A010673 A084099 A036665 * A036664 A045843 A181587

Adjacent sequences:  A053469 A053470 A053471 * A053473 A053474 A053475

KEYWORD

nonn

AUTHOR

Labos Elemer, Jan 14 2000

STATUS

approved

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Last modified December 13 20:27 EST 2019. Contains 329973 sequences. (Running on oeis4.)