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Search: id:A118255
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| A118255 |
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a(1)=1 as 1 is not prime, then a(n)=2*a(n-1) if n is prime, a(n)=2*a(n-1)+1 if n not prime. |
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8
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| 1, 2, 4, 9, 18, 37, 74, 149, 299, 599, 1198, 2397, 4794, 9589, 19179, 38359, 76718, 153437, 306874, 613749, 1227499, 2454999, 4909998, 9819997, 19639995, 39279991, 78559983, 157119967, 314239934, 628479869, 1256959738, 2513919477, 5027838955, 10055677911
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OFFSET
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1,2
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COMMENT
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In base 2 a(n)=concatenation for i=1 to n of A005171(i).
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EXAMPLE
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a(2)=2*1=2 as 2 is prime
a(3)=2*2=4 as 3 is prime
a(4)=2*4+1=9 as 4 composite
a(5)=2*9=18 as 5 is prime
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MAPLE
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f:=proc(n) option remember; if n=1 then RETURN(1); fi; if isprime(n) then 2*f(n-1) else 2*f(n-1)+1; fi; end; [N. J. A. Sloane]
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CROSSREFS
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Cf. A005171 A118256 A118257.
Sequence in context: A056185 A152537 A081253 this_sequence A019299 A052932 A018097
Adjacent sequences: A118252 A118253 A118254 this_sequence A118256 A118257 A118258
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KEYWORD
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nonn
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AUTHOR
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Pierre CAMI (pierrecami(AT)tele2.fr), Apr 19 2006
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EXTENSIONS
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Corrected by Omar E. Pol, Nov 08, 2007. Corrections verified by N. J. A. Sloane (njas(AT)research.att.com), Nov 17 2007.
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