cp's OEIS Frontend

A181687 Numbers n such that the number of odd divisors of (2n)^2 is an odd divisor of (2n)^2, and the number of even divisors of (2n)^2 is an even divisor of (2n)^2.

%I A181687 #6 Mar 31 2012 13:22:29
%S A181687 1,2,3,6,8,12,15,21,24,25,30,33,39,42,45,50,51,57,66,69,75,78,81,87,
%T A181687 90,93,96,102,111,114,120,123,128,129,138,141,150,159,162,168,174,177,
%U A181687 180,183,186,189,200,201,213,219,222,225,237,240,246,249,258,264,267,282,291,300
%N A181687 Numbers n such that the number of odd divisors of (2n)^2 is an odd divisor of (2n)^2, and the number of even divisors of (2n)^2 is an even divisor of (2n)^2.
%C A181687 A016742(a(n)) = A181795(n)
%p A181687 for j from 1 to 300 do
%p A181687    y:=(2*j)^2:evdiv:=0:oddiv:=0:
%p A181687    for k in divisors(y) do
%p A181687       if(k mod 2=0)then evdiv:=evdiv+1:else oddiv:=oddiv+1:fi:
%p A181687    od:
%p A181687    if(type(y/evdiv,integer) and type(y/oddiv,integer))then
%p A181687       print(j);
%p A181687    fi;
%p A181687 od:
%K A181687 easy,nonn
%O A181687 1,2
%A A181687 _Nathaniel Johnston_, Nov 17 2010