This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A280927 #15 Jan 02 2021 04:50:01 %S A280927 1735,2469,4341,4569,4989,5469,5637,5961,6879,7149,7407,8675,9969, %T A280927 11569,12949,13057,13089,13707,15829,15969,16407,18597,18969,19959, %U A280927 20109,20487,20721,21081,21309,21729,22107,22221,22513,23469,24355,25269,25617,26305,27021 %N A280927 Odd numbers k such that phi(k) and cototient(k) have the same prime signature. %C A280927 46347 = 3*7*2207 is the least term that has 3 distinct prime factors. %H A280927 Amiram Eldar, <a href="/A280927/b280927.txt">Table of n, a(n) for n = 1..10000</a> %e A280927 1735 is a term because phi(1735) = 1384 = 2^3 * 173 and cototient(1735) = 1735 - phi(1735) = 351 = 3^3 * 13. %t A280927 Select[Range[5, 30000, 2], Sort @ FactorInteger[(phi = EulerPhi[#])][[;;, 2]] == Sort @ FactorInteger[# - phi][[;;, 2]] &] (* _Amiram Eldar_, Jan 02 2021 *) %o A280927 (PARI) is(n) = vecsort(factor(eulerphi(n))[, 2]) == vecsort(factor(n-eulerphi(n))[, 2]) && n%2==1; %Y A280927 Cf. A000010, A051953. %K A280927 nonn %O A280927 1,1 %A A280927 _Altug Alkan_, Jan 10 2017