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A332444 Numbers k that are squares or twice-squares, but for which A087808(sigma(k)) is even. 2
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 (list; graph; refs; listen; history; text; internal format)
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:  A332437 A332438 A332443 * A332445 A332446 A332447

KEYWORD

nonn

AUTHOR

Antti Karttunen, Feb 13 2020

STATUS

approved

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Last modified April 5 00:43 EDT 2020. Contains 333238 sequences. (Running on oeis4.)