A239993 - OEIS

%I #8 Sep 08 2022 08:46:07

%S 1,4,7,9,13,16,19,25,28,31,37,43,49,52,61,64,67,73,76,79,81,91,97,100,

%T 103,109,112,121,124,127,133,139,148,151,157,163,169,172,175,181,193,

%U 199,208,211,217,223,225,229,241,244,247,256,259,268,271,277,283,289

%N Numbers n such that n*sigma(n) is not divisible by 6.

%C A000594(a(n)) cannot be 0 because 24 divides A000594(n) - n^4*sigma(n) for any n.

%t Select[Range[289], ! Divisible[#*DivisorSigma[1, #], 6] &]

%o (Magma) [n: n in [1..289] | not IsZero(n*SumOfDivisors(n) mod 6)];

%o (PARI) for(n=1, 289, if(!Mod(n*sigma(n), 6)==0, print1(n, ", ")));

%Y Supersequence of A002476. Cf. A000594.

%K nonn

%O 1,2

%A _Arkadiusz Wesolowski_, Mar 30 2014