A369225 - OEIS

A369225

Sum of the semiprimes less than n that do not divide n.

0, 0, 0, 0, 4, 4, 10, 6, 10, 19, 29, 19, 29, 29, 43, 54, 58, 43, 58, 44, 58, 79, 101, 91, 101, 126, 143, 134, 152, 121, 152, 148, 152, 185, 219, 235, 254, 254, 292, 317, 331, 290, 331, 305, 307, 331, 377, 367, 377, 391, 426, 447, 477, 462, 477, 514, 532, 589, 647, 612, 647, 647, 679

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OFFSET

1,5

LINKS

Table of n, a(n) for n=1..63.

FORMULA

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

MATHEMATICA

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

CROSSREFS

Cf. A001358 (semiprimes), A064911, A369224.

Sequence in context: A353267 A339336 A319056 * A050348 A134637 A078910

Adjacent sequences: A369222 A369223 A369224 * A369226 A369227 A369228

KEYWORD

nonn,easy

AUTHOR

Wesley Ivan Hurt, Jan 16 2024

STATUS

approved