A121998 - OEIS

%I #9 Mar 13 2018 22:13:18

%S 2,3,2,4,5,2,3,4,6,7,2,4,6,8,3,6,9,2,4,5,6,8,10,11,2,3,4,6,8,9,10,12,

%T 13,2,4,6,7,8,10,12,14,3,5,6,9,10,12,15,2,4,6,8,10,12,14,16,17,2,3,4,

%U 6,8,9,10,12,14,15,16,18,19,2,4,5,6,8,10,12,14,15,16,18,20,3,6,7,9,12,14,15

%N Table, n-th row gives numbers between 1 and n that have a common factor with n.

%C Row n contains numbers m <= n such that gcd(m,n) > 1, i.e., numbers m in the cototient of n. - _Michael De Vlieger_, Mar 13 2018

%H Michael De Vlieger, <a href="/A121998/b121998.txt">Table of n, a(n) for n = 2..12949</a> (rows 2 <= n <= 256).

%e 2;

%e 3;

%e 2,4;

%e 5;

%e 2,3,4,6;

%e 7;

%e ...

%t Table[Select[Range@ n, ! CoprimeQ[#, n] &], {n, 20}] // Flatten (* _Michael De Vlieger_, Mar 13 2018 *)

%Y Cf. A051953 (row lengths), A038566, A081520, A133995 (nondivisors in the cototient of n).

%K nonn,tabf

%O 2,1

%A _Franklin T. Adams-Watters_, Sep 11 2006