id:A071986 - OEIS Search Results

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A071986

Parity of Pi[n].

+0
4

0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1 (list; graph; listen)

	OFFSET	`1,1`
	COMMENT	`a(n)+a(n-1) = 1 if and only if n is prime - Benoit Cloitre (benoit7848c(AT)orange.fr), Jun 20 2002`
	LINKS	`Henry Lifchitz. Parity of Pi(n)`
	FORMULA	`a(n)=Mod[Pi[n], 2]`
	EXAMPLE	`a(100)=Mod[Pi[100],2]=1` `a(6)=1 since three primes [2,3,5] are <= 6 and three is odd.`
	MATHEMATICA	`Table[Mod[PrimePi[w], 2], {w, 1, 256}]`
	PROGRAM	`(PARI) a(n)=if(n<1, 0, if(isprime(n), 1-a(n-1), a(n-1)))`
	CROSSREFS	`Cf. A000720.` `Sequence in context: A130198 A104893 A104894 this_sequence A079944 A059652 A108736` `Adjacent sequences: A071983 A071984 A071985 this_sequence A071987 A071988 A071989`
	KEYWORD	`nonn`
	AUTHOR	`Labos E. (labos(AT)ana.sote.hu), Jun 17 2002`

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Last modified December 3 22:15 EST 2009. Contains 170310 sequences.

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