%I #20 Jun 19 2020 04:18:46

%S 1,2,4,5,8,9,10,13,16,17,18,20,25,26,29,32,34,36,37,40,41,45,49,50,52,

%T 53,58,61,64,68,72,73,74,80,81,82,89,90,97,98,100,101,104,106,109,113,

%U 116,117,121,122,128,136,137,144,146,148,149,153,157,160,162,164,169,173,178,180

%N Numbers n such that the sum of the divisors of n is not divisible by 4.

%C The complement of A248150; contains in particular A028982, the squares and twice the squares, for which sigma is odd.

%C The terms cannot have more than one odd prime factor to an odd power. Therefore this set has asymptotic density zero. The sequence grows faster than .75 n log(n). In particular: a(10) = 17, a(100) = 298, a(10^3) = 4724, a(10^4) = 66533, a(10^5) = 872434, a(10^6) = 10819205. - _M. F. Hasler_, Apr 26 2017

%H M. F. Hasler, <a href="/A248151/b248151.txt">Table of n, a(n) for n = 1..1000</a>

%o (PARI) for(n=1,999,sigma(n)%4&&print1(n","))

%Y Cf. A000203 (sum of divisors), A028982, A028983, A248150.

%Y Subsequence of A285801.

%K nonn

%O 1,2

%A _M. F. Hasler_, Oct 02 2014