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A209628 Number of squarefree numbers < n that are not prime. 0
1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 5, 5, 5, 5, 5, 5, 6, 7, 7, 7, 7, 8, 8, 8, 8, 9, 9, 9, 10, 11, 12, 12, 12, 13, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 19, 20, 20, 20, 20, 21, 21, 21, 22, 23, 23, 23, 24, 25, 25, 25, 25, 26 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Table of n, a(n) for n=1..74.

FORMULA

a(n) = A013928(n) - A000720(n).

MATHEMATICA

Accumulate[Table[Boole[SquareFreeQ[n]&&!PrimeQ[n]], {n, 1, 100}]]

CROSSREFS

Cf. A000720, A013928, A005117, A000040.

Sequence in context: A194621 A088004 A070548 * A132011 A054893 A090617

Adjacent sequences:  A209625 A209626 A209627 * A209629 A209630 A209631

KEYWORD

nonn

AUTHOR

Enrique Pérez Herrero, Mar 13 2012

STATUS

approved

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Last modified September 29 09:11 EDT 2020. Contains 337428 sequences. (Running on oeis4.)