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
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
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Nov 29 2003
STATUS
approved