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A097454 a(n) = (number of nonprimes <= n) - (number of primes <= n). 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,10

LINKS

Table of n, a(n) for n=1..93.

FORMULA

a(n) = 1 + A072731(n).

a(n) = n - 2*pi(n) =  n - 2*A000720(n). - Wesley Ivan Hurt, Jun 16 2013

a(n) - a(n-1) = 1 - 2*A010051(n) for n > 1. - Wesley Ivan Hurt, Dec 18 2018

a(n) = A062298(n) - A000720(n). - Michel Marcus, Jan 31 2019

EXAMPLE

a(7) = -1 because there are 3 nonprimes <= 7 (1,4 and 6) and 4 primes <= 7 (2,3,5 and 7).

MAPLE

with(numtheory): seq(n-2*pi(n), n=1..93); # Emeric Deutsch, Apr 01 2006

MATHEMATICA

qp=0; lst={}; Do[If[PrimeQ[n], AppendTo[lst, qp-=1], AppendTo[lst, qp+=1]], {n, 6!}]; lst (* Vladimir Joseph Stephan Orlovsky, Mar 15 2010 *)

Accumulate[ -1 + 2 * Boole /@ Not /@ PrimeQ @ Range @ 100] (* Federico Provvedi, Oct 06 2013 *)

PROG

(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) = { my(c, x); c=0; for(x=1, n, if(!isprime(x), c++); ); return(c) }

\\ pi(x) prime count function

pi(n) = { my(c, x); c=0; forprime(x=1, n, c++); return(c) }

CROSSREFS

Cf. A000720, A010051, A062298, A072731.

Sequence in context: A303780 A234022 A261273 * A139803 A058746 A080916

Adjacent sequences:  A097451 A097452 A097453 * A097455 A097456 A097457

KEYWORD

sign,easy

AUTHOR

Cino Hilliard, Aug 23 2004

STATUS

approved

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Last modified October 18 07:42 EDT 2019. Contains 328146 sequences. (Running on oeis4.)