cp's OEIS Frontend

A356171 Odd numbers that are not divisible by two consecutive prime numbers.

%I A356171 #10 Jul 29 2022 09:52:52
%S A356171 1,3,5,7,9,11,13,17,19,21,23,25,27,29,31,33,37,39,41,43,47,49,51,53,
%T A356171 55,57,59,61,63,65,67,69,71,73,79,81,83,85,87,89,91,93,95,97,99,101,
%U A356171 103,107,109,111,113,115,117,119,121,123,125,127,129,131,133,137,139,141,145,147,149,151,153,155,157,159,161,163
%N A356171 Odd numbers that are not divisible by two consecutive prime numbers.
%C A356171 Numbers k such that k and the smallest positive x such that k divides x*A003961(x) are coprime, where A003961 is fully multiplicative with a(p) = nextprime(p).
%H A356171 Antti Karttunen, <a href="/A356171/b356171.txt">Table of n, a(n) for n = 1..28906; terms up to 65537</a>
%H A356171 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>
%o A356171 (PARI)
%o A356171 A003961(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };
%o A356171 A356172(n) = for(k=1, oo, if((k*A003961(k))%n==0, return(1==gcd(n,k))));
%o A356171 isA356171(n) = A356172(n);
%Y A356171 Odd terms in A319630.
%Y A356171 Positions of 1's in A356166, positions of 0's in A356169.
%Y A356171 Cf. A003961, A356164, A356172 (characteristic function).
%K A356171 nonn
%O A356171 1,2
%A A356171 _Antti Karttunen_, Jul 28 2022