A241480 - OEIS

%I #7 Jun 05 2015 07:06:55

%S 2,3,4,5,7,8,9,12,13,18,19,22,27,29,32,36,37,43,45,48,49,50,61,64,67,

%T 68,72,73,75,80,81,82,91,98,100,101,104,106,109,116,121,122,128,129,

%U 133,134,137,144,146,148,149,152,156,157,160,162,163,169,171,173

%N Numbers such that the GCD of the x's that satisfy sigma(x)=sigma(n) is not equal to 1.

%C Apart from 1, all terms of A211656 belong here since the solutions to sigma(x)=sigma(n) form a singleton and thus their GCD is n itself.

%F Numbers such that A241479(n) is not equal to 1.

%o (PARI) sigv(n) =  select(i->sigma(i) == n, vector(n, i, i));

%o isok(n) = (gcd(sigv(sigma(n))) != 1);

%Y Cf. A000203, A211656, A241479.

%K nonn

%O 1,1

%A _Michel Marcus_, Apr 23 2014