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

1,1

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)

Prog

(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];

Crossrefs

Setwise difference of A028982 \ A332443.

Cf. A000203, A087808, A332224, A332225.

Sequence in context: A128324 A264572 A279692 * A323145 A071387 A330782

Adjacent sequences: A332441 A332442 A332443 * A332445 A332446 A332447

Keyword

nonn

Author

Antti Karttunen, Feb 13 2020

Status

approved