A388985 Numbers k such that {sum of unitary divisors of k} plus {sum of squarefree divisors of k} does not exceed 2*k.

1, 4, 8, 9, 16, 24, 25, 27, 32, 36, 40, 45, 48, 49, 50, 54, 56, 63, 64, 72, 75, 80, 81, 88, 96, 98, 99, 100, 104, 108, 112, 117, 121, 125, 128, 135, 136, 144, 147, 152, 153, 160, 162, 169, 171, 175, 176, 184, 189, 192, 196, 200, 207, 208, 216, 224, 225, 232, 240, 242, 243, 245, 248, 250, 252, 256, 261, 272, 275

Offset

1,2

Comments

Numbers k for which A325973(k) <= k, or equally, A325977(k) <= 0.

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Formula

{k | A034448(k)+A048250(k) <= 2*k}.

Prog

(PARI)
A034448(n) = { my(f=factorint(n)); prod(k=1, #f~, 1+(f[k, 1]^f[k, 2])); };
A048250(n) = factorback(apply(p -> p+1, factor(n)[, 1]));
is_A388985(k) = ((A034448(k)+A048250(k)) <= 2*k);

Crossrefs

Cf. A034448, A048250, A325973.

Positions of terms <= 0 in A325977.

Disjoint union of A325963 and A388986.

Sequence in context: A243180 A100657 A372280 * A361204 A245080 A212164

Adjacent sequences: A388982 A388983 A388984 * A388986 A388987 A388988

Keyword

nonn

Author

Antti Karttunen, Sep 29 2025

Status

approved