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A097454
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(Number of nonprimes <= n) - (number of primes <= n).
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1
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1, 0, -1, 0, -1, 0, -1, 0, 1, 2, 1, 2, 1, 2, 3, 4, 3, 4, 3, 4, 5, 6, 5, 6, 7, 8, 9, 10, 9, 10, 9, 10, 11, 12, 13, 14, 13, 14, 15, 16, 15, 16, 15, 16, 17, 18, 17, 18, 19, 20, 21, 22, 21, 22, 23, 24, 25, 26, 25, 26, 25, 26, 27, 28, 29, 30, 29, 30, 31, 32, 31, 32, 31, 32, 33, 34, 35, 36, 35, 36, 37, 38, 37, 38, 39, 40, 41, 42, 41, 42, 43, 44, 45
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OFFSET
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1,10
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LINKS
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Table of n, a(n) for n=1..93.
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FORMULA
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a(n) = n - 2pi(n). [Wesley Ivan Hurt, Jun 16 2013]
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EXAMPLE
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a(7)=-1 because there are 3 nonprimes <=7 (1,4 and 6) and 4 primes <=7 (2,3,5 and 7).
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MAPLE
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with(numtheory): seq(n-2*pi(n), n=1..93); - Emeric Deutsch, Apr 01 2006
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MATHEMATICA
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qp=0; lst={}; Do[If[PrimeQ[n], AppendTo[lst, qp-=1], AppendTo[lst, qp+=1]], {n, 6!}]; lst [From Vladimir Joseph Stephan Orlovsky, Mar 15 2010]
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PROG
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(PARI) compsmprimes(n) = { for(x=1, n, y=composites(x) - pi(x); print1(y", ") ) } \The number of composite numbers less than or equal to n composites(n) = { local(c, x); c=0; for(x=1, n, if(!isprime(x), c++); ); return(c) } \pi(x) prime count function pi(n) = { local(c, x); c=0; forprime(x=1, n, c++); return(c) }
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CROSSREFS
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(Number of composites <= n) - (number of primes <= n) is A072731. a(n)=1+A072731(n).
Sequence in context: A069003 A087855 A083409 * A139803 A058746 A080916
Adjacent sequences: A097451 A097452 A097453 * A097455 A097456 A097457
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KEYWORD
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sign,changed
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AUTHOR
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Cino Hilliard (hillcino368(AT)gmail.com), Aug 23 2004
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STATUS
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approved
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