A331019 - OEIS

%I #12 Jan 09 2020 11:52:04

%S 1,15,1,8,1,144,1,16,1,1,1,8,1,255,3,16,1,12,1,2,7,1,1,288,1,18,21,8,

%T 1,84,1,13,1,11,1,4096,1,4,3,270,1,2448,1,2,3,1,1,16,1,420,3,1,1,124,

%U 3,16,3,128,1,616,1,85,3,16,1,1,1,8,3,1,1,32,1,64

%N a(n) is the least k such that the denominator(sigma(sigma(k*n))/(k*n)) equals n.

%C a(n) is the least k such that the A318060(k*n) equals n.

%H Ray Chandler, <a href="/A331019/b331019.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A331033(n)/n.

%o (PARI) a(n) = my(k=n); while (denominator(sigma(sigma(k))/k) != n, k+=n); k/n;

%Y Cf. A000203 (sigma), A051027 (sigma(sigma)), A318060.

%Y Cf. A019278, A330598, A331033.

%K nonn

%O 1,2

%A _Ray Chandler_, Jan 09 2020