A332444 Numbers k that are squares or twice-squares, but for which A087808(sigma(k)) is even.

2, 8, 32, 36, 72, 98, 128, 144, 162, 196, 225, 242, 288, 289, 324, 484, 512, 576, 882, 968, 1058, 1152, 1444, 1458, 1521, 1681, 1764, 1922, 1936, 2048, 2178, 2304, 2500, 2809, 2888, 2916, 3025, 3528, 3698, 3872, 4418, 4608, 4802, 5000, 5329, 5776, 5832, 6498, 7056, 7396, 7569, 7688, 7744, 7921, 7938, 8192, 8281

Offset: 1

Author

Antti Karttunen, Feb 13 2020

Keywords

• nonn

Comments

Numbers k for which A000203(k) is odd and A332224(k) is even.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..19515
• Index entries for sequences related to sigma(n)

Crossrefs

Setwise difference of A028982 \ A332443.

Cf. A000203, A087808, A332224, A332225.

Programs

PARI

A087808(n) = if(n<1, 0, if(n%2==0, 2*A087808(n/2), A087808((n-1)/2)+1));
isA332444(n) = (((!(n%2)&&issquare(n/2))||issquare(n)) && !(A087808(sigma(n))%2));
A332444list(u) = { my(v1=vector(2*u,n,2*(n^2)), v2=vector(sqrtint(v1[#v1]),n,n^2)); select(isA332444,Vec(setunion(v1,v2))); };
v332444 = A332444list(12000);
A332444(n) = v332444[n];