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Search: id:A073798
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| A073798 |
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pi(n) is a power of 2, where pi(n)=A000720(n) is the number of primes <= n. |
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+0
5
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| 2, 3, 4, 7, 8, 9, 10, 19, 20, 21, 22, 53, 54, 55, 56, 57, 58, 131, 132, 133, 134, 135, 136, 311, 312, 719, 720, 721, 722, 723, 724, 725, 726, 1619, 1620, 3671, 3672, 8161, 8162, 8163, 8164, 8165, 8166, 17863, 17864, 17865, 17866, 17867, 17868, 17869, 17870
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The numbers occur in blocks of consecutive integers: 2, 3-4, 7-10, 19-22, ...; the n-th block starts at the 2^n-th prime (A033844) and ends just before the (2^n + 1)-th prime (A051439).
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EXAMPLE
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10 is in the sequence since pi(10)=4=2^2.
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MATHEMATICA
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pow2[n_] := n==1||(n>1&&IntegerQ[n/2]&&pow2[n/2]); Select[Range[20000], pow2[PrimePi[ # ]]&]
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CROSSREFS
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Cf. A000079, A000720, A015910, A073797, A073799.
Sequence in context: A047227 A112965 A070942 this_sequence A124375 A037080 A022162
Adjacent sequences: A073795 A073796 A073797 this_sequence A073799 A073800 A073801
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Aug 14 2002
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EXTENSIONS
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Edited by Dean Hickerson (dean(AT)math.ucdavis.edu), Aug 15 2002
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