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Search: id:A122669
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| A122669 |
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Number of nontrivial arithmetic progressions of primes between n and 2n. |
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1
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| 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 3, 3, 3, 4, 4, 3, 3, 3, 3, 4, 5, 5, 5, 8, 8, 8, 8, 7, 8, 8, 8, 5, 6, 6, 6, 6, 6, 7, 8, 8, 10, 10, 10, 8, 8, 5, 5, 7, 7, 9, 9, 7, 8, 9, 9, 7, 7, 7, 8, 11, 11, 11, 12, 9, 9, 12, 12, 14, 14, 14, 16, 16, 16, 14, 15, 15, 15, 15, 15
(list; graph; listen)
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OFFSET
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1,27
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COMMENT
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Count of subsets of at least 3 primes in range that are arithmetic progressions.
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EXAMPLE
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a(15)=1 because primes between 15 and 30 are {17, 19, 23, 29} and {17, 23, 29} is an arithmetic progression.
a(27)=a(28)=a(29)=3 because {29, 31, 37, 41, 43, 47, 53} includes {29, 41, 53}, {31, 37, 43}, {41, 47, 53}.
a(30)=4 because {31, 37, 41, 43, 47, 53, 59} includes {31, 37, 43}, {41, 47, 53}, {47, 53, 59}, {41, 47, 53,
59}.
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CROSSREFS
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Sequence in context: A079108 A165605 A128112 this_sequence A071942 A134849 A096056
Adjacent sequences: A122666 A122667 A122668 this_sequence A122670 A122671 A122672
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KEYWORD
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nonn
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AUTHOR
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Giovanni Teofilatto (g.teofilatto(AT)tiscalinet.it), Sep 24 2006
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EXTENSIONS
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Edited and extended by Ray Chandler (rayjchandler(AT)sbcglobal.net), Sep 26 2006
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