A033271 Number of odd nonprimes <= n.

1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10, 11, 11, 12, 12, 12, 12, 13, 13, 14, 14, 14, 14, 14, 14, 15, 15, 16, 16, 16, 16, 17, 17, 17, 17, 17, 17, 18, 18, 19, 19, 19, 19

Offset

1,9

Links

Table of n, a(n) for n=1..80.

Formula

If n>1, then a(n) = floor((n+1)/2) - primepi(n) + 1, where primepi denotes the number of primes <= n a(n)/n is convergent against 0.5. - Stefan Steinerberger, May 09 2006

Mathematica

Insert[Table[Floor[(n + 1)/2] - PrimePi[n] + 1, {n, 2, 80}], 1, 1] (* Stefan Steinerberger, May 09 2006 *)
nn=101; With[{nps=Complement[Range[1, nn, 2], Prime[Range[PrimePi[nn]]]]}, Table[Count[nps, _?(#<=n&)], {n, nn}]]  (* Harvey P. Dale, Mar 23 2011 *)
Accumulate[Table[If[OddQ[n]&&!PrimeQ[n], 1, 0], {n, 100}]] (* Harvey P. Dale, Jan 16 2019 *)

Crossrefs

Sequence in context: A194699 A262694 A137588 * A290792 A279757 A251550

Adjacent sequences: A033268 A033269 A033270 * A033272 A033273 A033274

Keyword

nonn

Author

N. J. A. Sloane

Extensions

More terms from Stefan Steinerberger, May 09 2006

Status

approved