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A280927 Odd numbers k such that phi(k) and cototient(k) have the same prime signature. 2
1735, 2469, 4341, 4569, 4989, 5469, 5637, 5961, 6879, 7149, 7407, 8675, 9969, 11569, 12949, 13057, 13089, 13707, 15829, 15969, 16407, 18597, 18969, 19959, 20109, 20487, 20721, 21081, 21309, 21729, 22107, 22221, 22513, 23469, 24355, 25269, 25617, 26305, 27021 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

46347 = 3*7*2207 is the least term that has 3 distinct prime factors.

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

EXAMPLE

1735 is a term because phi(1735) = 1384 = 2^3 * 173 and cototient(1735) = 1735 - phi(1735) = 351 = 3^3 * 13.

MATHEMATICA

Select[Range[5, 30000, 2], Sort @ FactorInteger[(phi = EulerPhi[#])][[;; , 2]] == Sort @ FactorInteger[# - phi][[;; , 2]] &] (* Amiram Eldar, Jan 02 2021 *)

PROG

(PARI) is(n) = vecsort(factor(eulerphi(n))[, 2]) == vecsort(factor(n-eulerphi(n))[, 2]) && n%2==1;

CROSSREFS

Cf. A000010, A051953.

Sequence in context: A113701 A283385 A083606 * A095847 A253696 A253703

Adjacent sequences:  A280924 A280925 A280926 * A280928 A280929 A280930

KEYWORD

nonn

AUTHOR

Altug Alkan, Jan 10 2017

STATUS

approved

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Last modified September 22 02:38 EDT 2021. Contains 347605 sequences. (Running on oeis4.)