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Search: id:A155879
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| A155879 |
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Smallest positive composite number such that a(n)-n is also composite and such that a(n)<a(n+1) |
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+0
1
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| 4, 9, 10, 12, 14, 15, 16, 21, 22, 24, 25, 26, 27, 28, 30, 33, 34, 35, 36, 39, 40, 42, 44, 45, 46, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100, 104, 105, 106, 108
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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a(0)=4. Subtracting n=0 from a(0) gives 4-0=4, which is a composite number; subtracting n=1 from a(1) gives 9-1=8, which is a composite number; subtracting n=2 from a(2) gives 12-2=10, which is a composite number; subtracting n=3 from a(3) gives 15-3=12, which is a composite number; etc.
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MAPLE
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isA002808 := proc(n) option remember; RETURN(n>= 4 and not isprime(n)) ; end: A155879:= proc(n) option remember; local a; if n = 0 then 4; else for a from procname(n-1)+1 do if isA002808(a) and isA002808(a-n) then RETURN(a) ; fi; od: fi; end: seq(A155879(n), n=0..100) ; [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 31 2009]
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CROSSREFS
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A155875
Sequence in context: A062371 A046030 A125726 this_sequence A086390 A038029 A020672
Adjacent sequences: A155876 A155877 A155878 this_sequence A155880 A155881 A155882
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KEYWORD
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base,easy,nonn
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AUTHOR
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Eric Angelini (eric.angelini(AT)skynet.be), Jan 29 2009
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EXTENSIONS
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Corrected from a(2) on by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 31 2009
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