A209628 Number of squarefree numbers < n that are not prime.

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

Offset

1,6

Links

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

Formula

a(n) = A013928(n+1) - A000720(n). [Corrected by Georg Fischer, Dec 13 2022]

Mathematica

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

Crossrefs

Cf. A000720, A013928, A005117, A000040.

Sequence in context: A194621 A088004 A070548 * A132011 A363822 A054893

Adjacent sequences: A209625 A209626 A209627 * A209629 A209630 A209631

Keyword

nonn

Author

Enrique Pérez Herrero, Mar 13 2012

Status

approved