A368424 - OEIS

%I #27 Jan 25 2024 02:41:03

%S 4,11,18,20,23,28,35,43,48,52,83,95,100,119,131,138,148,155,162,166,

%T 172,179,191,196,204,210,214,239,251,253,268,292,299,300,316,323,342,

%U 359,371,378,388,419,431,443,460,463,491,500,508,515,537,556,564,575

%N Numbers k such that gcd(A019320(k), A019321(k)) > 1.

%C The corresponding greatest common divisors are given in A368425.

%H Robert Israel, <a href="/A368424/b368424.txt">Table of n, a(n) for n = 1..1000</a>

%e a(1) = 4 since A019320(4) = 5 and A019321(4) = 10.

%p select(k -> igcd(numtheory:-cyclotomic(k,2),

%p numtheory:-cyclotomic(k,3)) > 1, [$1..1000]); # _Robert Israel_, Dec 26 2023

%t Select[Range[600],GCD[Cyclotomic[#,2],Cyclotomic[#,3]]>1&] (* _Stefano Spezia_, Dec 26 2023 *)

%o (PARI) for(n=1,1000,if(gcd(polcyclo(n,2),polcyclo(n,3))>1,print1(n,", ")))

%Y Cf. A019320, A019321, A191609 (prime factors of such gcds), A368425.

%K nonn

%O 1,1

%A _Tomohiro Yamada_, Dec 24 2023