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A090406 a(n) = PrimePi(n+3) - PrimePi(n). 3
2, 2, 1, 2, 1, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 2, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 2, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 2, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 2, 1, 1, 0, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 2, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) <= 2, with equality if and only if n=1 or n+1 is in A001359. - Robert Israel, Aug 14 2015

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Hardy-Littlewood Conjectures

FORMULA

a(n) = A010051(n+1) + A010051(n+2) + A010051(n+3). - Robert Israel, Aug 14 2015

MAPLE

B:= [seq(numtheory:-pi(n), n=1..103)]:

B[4..-1] - B[1..-4]; # Robert Israel, Aug 14 2015

MATHEMATICA

Last[#]-First[#]&/@Partition[PrimePi[Range[110]], 4, 1] (* Harvey P. Dale, Feb 24 2013 *)

CROSSREFS

Cf. A000720, A001359, A010051, A080545, A090405.

Sequence in context: A298948 A085906 A221649 * A152723 A237497 A281191

Adjacent sequences:  A090403 A090404 A090405 * A090407 A090408 A090409

KEYWORD

nonn

AUTHOR

Eric W. Weisstein, Nov 29 2003

STATUS

approved

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Last modified October 14 09:25 EDT 2019. Contains 327995 sequences. (Running on oeis4.)