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A071986
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Parity of Pi[n].
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5
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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; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(n)+a(n-1) = 1 if and only if n is prime - Benoit Cloitre (benoit7848c(AT)orange.fr), Jun 20 2002
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LINKS
| Henry Lifchitz. Parity of Pi(n)
Terence Tao et. al., Prime counting function, Polymath1 project (2009)
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FORMULA
| a(n) = pi(n) mod 2.
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EXAMPLE
| a(6)=1 since three primes [2,3,5] are <= 6 and three is odd.
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MATHEMATICA
| Table[Mod[PrimePi[w], 2], {w, 1, 256}]
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PROG
| (PARI) a(n)=primepi(n)%2
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CROSSREFS
| Cf. A000720.
Sequence in context: A104893 A104894 A168393 * A079944 A059652 A108736
Adjacent sequences: A071983 A071984 A071985 * A071987 A071988 A071989
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KEYWORD
| nonn,easy
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Jun 17 2002
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EXTENSIONS
| Edited by Charles R Greathouse IV, Feb 19 2011
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