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 A379851 #21 Feb 05 2025 21:57:50 %S A379851 3,5,7,9,10,11,13,14,15,17,19,20,21,22,23,25,26,27,28,29,30,31,33,34, %T A379851 35,37,38,39,40,41,42,43,44,45,46,47,49,50,51,52,53,55,56,57,58,59,60, %U A379851 61,62,63,65,66,67,68,69,70,71,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89 %N A379851 Numbers k such that phi(k) does not divide k. Complement of A007694. %C A379851 Let PHI(n) the set of all numbers x such there is a k-fold iteration of Euler's totient function phi = A000010 on x resulting in n. The numbers a(n) are exactly the numbers for which PHI(a(n)) is a finite set (possibly empty). %C A379851 Contains A007617. %H A379851 Robert Israel, <a href="/A379851/b379851.txt">Table of n, a(n) for n = 1..10000</a> %p A379851 filter:= n -> n mod numtheory:-phi(n) <> 0: %p A379851 select(filter, [$1..100]); # _Robert Israel_, Feb 04 2025 %t A379851 Select[Range[100], ! Divisible[#, EulerPhi[#]] &] (* _Amiram Eldar_, Jan 08 2025 *) %Y A379851 Cf. A000010, A007617. Complement of A007694. %K A379851 nonn %O A379851 1,1 %A A379851 _Franz Vrabec_, Jan 04 2025