A369224 Number of semiprimes less than n that do not divide n.

0, 0, 0, 0, 1, 1, 2, 1, 2, 3, 4, 2, 4, 4, 5, 5, 6, 4, 6, 4, 6, 7, 8, 6, 8, 9, 9, 8, 10, 7, 10, 9, 10, 11, 12, 10, 13, 13, 14, 13, 15, 12, 15, 13, 13, 15, 16, 14, 16, 15, 17, 16, 18, 16, 18, 17, 19, 20, 21, 17, 21, 21, 20, 21, 22, 20, 23, 21, 23, 21, 24, 21, 24, 24, 23

Offset

1,7

Links

Table of n, a(n) for n=1..75.

Formula

a(n) = Sum_{k=1..n} c(k) * (ceiling(n/k) - floor(n/k)), where c = A064911.

Mathematica

Table[Sum[KroneckerDelta[PrimeOmega[k], 2] (Ceiling[n/k] - Floor[n/k]), {k, n}], {n, 100}]

Crossrefs

Cf. A001358 (semiprimes), A064911, A369225.

Sequence in context: A328365 A033787 A165073 * A176846 A144735 A304734

Adjacent sequences: A369221 A369222 A369223 * A369225 A369226 A369227

Keyword

nonn,easy

Author

Wesley Ivan Hurt, Jan 16 2024

Status

approved