A374475 - OEIS

%I #6 Aug 06 2024 16:38:20

%S 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 50,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,83,85,87,89,91,93,95,

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

%H Antti Karttunen, <a href="/A374475/b374475.txt">Table of n, a(n) for n = 1..12000</a>

%o (PARI)

%o A020639(n) = if(1==n,n,vecmin(factor(n)[, 1]));

%o A053669(n) = forprime(p=2, , if(n%p, return(p))); \\ From A053669

%o A374474(n) = (A020639(sigma(n))==A053669(n));

%o isA374475 = A374474;

%Y Cf. A000203, A020639, A053669, A374474 (characteristic function), A374476 (composite terms).

%Y Cf. also A370125.

%K nonn

%O 1,1

%A _Antti Karttunen_, Aug 06 2024