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A033271
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Number of odd nonprimes <= n.
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0
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,9
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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 (stefan.steinerberger(AT)gmail.com), May 09 2006
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MATHEMATICA
| Insert[Table[Floor[(n + 1)/2] - PrimePi[n] + 1, {n, 2, 80}], 1, 1] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), May 09 2006
nn=101; With[{nps=Complement[Range[1, nn, 2], Prime[Range[PrimePi[nn]]]]}, Table[Count[nps, _?(#<=n&)], {n, nn}]] (* From Harvey P. Dale, Mar 23 2011 *)
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CROSSREFS
| Sequence in context: A054895 A194699 A137588 * A004052 A051742 A134119
Adjacent sequences: A033268 A033269 A033270 * A033272 A033273 A033274
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), May 09 2006
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