cp's OEIS Frontend

A332443 Numbers k such that A332224(k) = A087808(sigma(k)) is odd.

%I A332443 #16 Feb 15 2020 08:04:59
%S A332443 1,4,9,16,18,25,49,50,64,81,100,121,169,200,256,338,361,392,400,441,
%T A332443 450,529,578,625,648,676,722,729,784,800,841,900,961,1024,1089,1156,
%U A332443 1225,1250,1296,1352,1369,1568,1600,1682,1800,1849,2025,2116,2209,2312,2401,2450,2592,2601,2704,2738,3042,3136,3200,3249,3362,3364,3481,3600
%N A332443 Numbers k such that A332224(k) = A087808(sigma(k)) is odd.
%C A332443 Numbers k such that A332224(k) is odd, or equally, that A332448(k) is zero.
%H A332443 Antti Karttunen, <a href="/A332443/b332443.txt">Table of n, a(n) for n = 1..26213</a>
%H A332443 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%o A332443 (PARI)
%o A332443 A087808(n) = if(n<1, 0, if(n%2==0, 2*A087808(n/2), A087808((n-1)/2)+1));
%o A332443 isA332443(n) = (A087808(sigma(n))%2);
%o A332443 A332443list(u) = { my(v1=vector(2*u,n,2*(n^2)), v2=vector(sqrtint(v1[#v1]),n,n^2)); select(isA332443,Vec(setunion(v1,v2))); };
%o A332443 v332443 = A332443list(8192);
%o A332443 A332443(n) = v332443[n];
%Y A332443 Cf. A000203, A087808, A332224, A332225, A332444.
%Y A332443 Subsequence of A028982. Positions of zeros in A332448.
%K A332443 nonn
%O A332443 1,2
%A A332443 _Antti Karttunen_, Feb 13 2020