A370788 Cubefull numbers with an odd number of prime factors (counted with multiplicity).

8, 27, 32, 125, 128, 243, 343, 432, 512, 648, 1331, 1728, 2000, 2048, 2187, 2197, 2592, 3125, 3888, 4913, 5000, 5488, 5832, 6859, 6912, 8000, 8192, 10125, 10368, 12167, 15552, 16807, 16875, 19208, 19683, 20000, 21296, 21952, 23328, 24389, 27000, 27648, 27783, 29791

Offset: 1

Author

Amiram Eldar, Mar 02 2024

Keywords

• nonn
• easy

Comments

Jakimczuk (2024) proved:

The number of terms that do not exceed x is N(x) = c * x^(1/3) / 2 + o(x^(1/3)) where c = A362974.

The relative asymptotic density of this sequence within the cubefull numbers is 1/2.

In general, the relative asymptotic density of the s-full numbers (numbers whose exponents in their prime factorization are all >= s) with an odd number of prime factors (counted with multiplicity) within the s-full numbers is 1/2 when s is odd.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Rafael Jakimczuk, Arithmetical Functions over the Powerful Part of an Integer, ResearchGate, 2024.

Crossrefs

Intersection of A036966 and A026424.

Complement of A370787 within A036966.

Subsequence of A370786.

Cf. A362974.

Programs

Mathematica

q[n_] := Module[{e = FactorInteger[n][[;; , 2]]}, AllTrue[e, # > 2 &] && OddQ[Total[e]]]; Select[Range[30000], q]

PARI

is(n) = {my(e = factor(n)[, 2]); n > 1 && vecmin(e) > 2 && vecsum(e)%2;}