login
A369224
Number of semiprimes less than n that do not divide n.
1
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
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
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Jan 16 2024
STATUS
approved