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 A068422 #19 Apr 24 2025 02:14:42 %S A068422 2,3,5,6,7,10,11,13,14,17,19,22,23,26,29,31,34,37,38,41,43,46,47,53, %T A068422 58,59,61,62,67,71,73,74,79,82,83,86,89,94,97,99,101,103,106,107,109, %U A068422 113,118,122,127,131,134,137,139,142,146,149,151,157,158,163,166,167,168 %N A068422 Numbers k such that k-phi(k) divides sigma(k). %C A068422 If p is an odd prime, p and 2*p are in the sequence but there are some other kinds of numbers as 99 or 168. %H A068422 Robert Israel, <a href="/A068422/b068422.txt">Table of n, a(n) for n = 1..10000</a> %p A068422 filter:= proc(n) uses numtheory; type(sigma(n)/(n - phi(n)), integer) end proc: %p A068422 select(filter, [$2..1000]); # _Robert Israel_, May 03 2019 %t A068422 Select[Range[2,200],Divisible[DivisorSigma[1,#], #-EulerPhi[#]]&] (* _Harvey P. Dale_, Mar 14 2011 *) %o A068422 (PARI) isok(k) = if(k == 1, 0, my(f = factor(k)); !(sigma(f) % (k-eulerphi(f)))); \\ _Amiram Eldar_, Apr 24 2025 %Y A068422 Cf. A000010, A000203, A055164. %K A068422 easy,nonn %O A068422 1,1 %A A068422 _Benoit Cloitre_, Mar 02 2002