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Search: id:A162308
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| 0, 7, 9, 11, 11, 13, 15, 15, 15, 15, 19, 19, 19, 23, 23, 23, 23, 29, 29, 31, 33, 33, 33, 35, 37, 37, 39, 39, 39, 41, 41, 41, 41, 41, 41, 41, 41, 41, 41, 45, 45, 45, 45, 47, 47, 47, 47, 47, 47, 47, 49, 49, 49, 49, 51, 51, 51, 53, 53, 55, 57, 57, 59, 59, 59, 59, 59, 59, 59
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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a(2)=7 counts the numbers 3, 5, 7, 11, 13, 17, 19 below 23=A007510(2).
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MAPLE
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isA007510 := proc(n) RETURN(isprime(n) and not isprime(n-2) and not isprime(n+2)) ; end:
isA001097 := proc(n) RETURN(isprime(n) and (isprime(n-2) or isprime(n+2)) ) ; end:
A007510 := proc(n) local a; if n = 1 then 2; else for a from procname(n-1)+1 do if isA007510(a) then RETURN(a) ; fi; od: fi; end:
A162308 := proc(n) local a, k; a := 0 ; for k from 3 to A007510(n)-1 do if isA001097(k) then a := a+1; fi; od; a; end:
seq(A162308(n), n=1..120) ; # R. J. Mathar, Jul 02 2009
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CROSSREFS
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Cf. A000040, A073425.
Sequence in context: A117933 A112162 A058483 this_sequence A108815 A161992 A167377
Adjacent sequences: A162305 A162306 A162307 this_sequence A162309 A162310 A162311
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), Jul 01 2009
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EXTENSIONS
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Edited by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 02 2009
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