cp's OEIS Frontend

A374475 Numbers k such that the least prime dividing the sum of divisors of k is equal to the least prime not dividing k.

%I A374475 #6 Aug 06 2024 16:38:20
%S A374475 2,3,5,7,8,11,13,15,17,19,21,23,27,29,31,32,33,35,37,39,41,43,45,47,
%T A374475 50,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,83,85,87,89,91,93,95,
%U A374475 97,98,99,101,103,105,107,109,111,113,115,117,119,123,125,127,128,129,131,133,135,137,139,141,143,145,147
%N A374475 Numbers k such that the least prime dividing the sum of divisors of k is equal to the least prime not dividing k.
%H A374475 Antti Karttunen, <a href="/A374475/b374475.txt">Table of n, a(n) for n = 1..12000</a>
%o A374475 (PARI)
%o A374475 A020639(n) = if(1==n,n,vecmin(factor(n)[, 1]));
%o A374475 A053669(n) = forprime(p=2, , if(n%p, return(p))); \\ From A053669
%o A374475 A374474(n) = (A020639(sigma(n))==A053669(n));
%o A374475 isA374475 = A374474;
%Y A374475 Cf. A000203, A020639, A053669, A374474 (characteristic function), A374476 (composite terms).
%Y A374475 Cf. also A370125.
%K A374475 nonn
%O A374475 1,1
%A A374475 _Antti Karttunen_, Aug 06 2024