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Search: id:A142350
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| A142350 |
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Nonprimes of the form n/4*(c(n)-r(n)), where c(n)=n-th composite and r(n)=n-th nonprime. |
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1
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| 1, 4, 8, 6, 8, 14, 10, 18, 20, 21, 15, 24, 25, 27, 28, 30, 21, 32, 22, 34, 24, 25, 26, 42, 44, 45, 46, 48, 49, 50, 34, 52, 54, 55, 56, 38, 58, 40, 42, 64, 65, 66, 68, 46, 48, 75, 51, 77, 52, 80, 81, 82, 84, 86, 87, 88, 90, 91, 92, 93, 63, 95, 96, 98, 66, 100, 102, 104, 70, 72
(list; graph; listen)
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OFFSET
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1,2
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EXAMPLE
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If n=12, then 12/4*(c(12)-r(12))=3/(21-18)=1=a(1).
If n=48, then 48/4*(c(48)-r(48))=12/(68-65)=4=a(2).
If n=64, then 64/4*(c(64)-r(64))=16/(76-74)=8=a(3).
If n=72, then 72/4*(c(72)-r(72))=18/(98-95)=6=a(4).
If n=96, then 96/4*(c(96)-r(96))=24/(117-115)=12=a(5), etc.
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MAPLE
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A141468 := proc(n) option remember ; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A002808 := proc(n) option remember ; A141468(n+2) ; end: for n from 1 to 3000 do p := n/(A002808(n)-A141468(n))/4 ; if type(p, 'integer') then if not isprime(p) then printf("%d, ", p) ; fi; fi; od: [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 23 2009]
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CROSSREFS
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Cf. A002808, A141468.
Sequence in context: A155741 A063808 A081455 this_sequence A011515 A005531 A064494
Adjacent sequences: A142347 A142348 A142349 this_sequence A142351 A142352 A142353
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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), Sep 21 2008
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EXTENSIONS
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Corrected and extended by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 23 2009
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