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Search: id:A059788
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| A059788 |
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Largest prime <= 2*prime(n). |
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+0
2
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| 3, 5, 7, 13, 19, 23, 31, 37, 43, 53, 61, 73, 79, 83, 89, 103, 113, 113, 131, 139, 139, 157, 163, 173, 193, 199, 199, 211, 211, 223, 251, 257, 271, 277, 293, 293, 313, 317, 331, 337, 353, 359, 379, 383, 389, 397, 421, 443, 449, 457, 463, 467, 479, 499, 509, 523
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Also, smallest member of the first pair of consecutive primes such that between them is a composite number divisible by the n-th prime. - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Sep 25 2002
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EXAMPLE
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n=18: p(18)=61, so the largest prime before 122 is a(18)=113.
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MAPLE
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with(numtheory): [seq(prevprime(2*ithprime(k)), k=1..256)];
for i from 1 to 122 do j := 1:a[i] := -1:while(true) do for k from ithprime(j)+1 to ithprime(j+1)-1 do if((k mod ithprime(i))=0) then a[i] := ithprime(j):break:fi:od: j := j+1: if(a[i]<>-1) then break:fi:od:od:seq(a[l], l=1..122);
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MATHEMATICA
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a[n_] := Prime[PrimePi[2Prime[n]]]
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CROSSREFS
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Cf. A005382, A005383, A005384, A005385, A055496, A006992, A052248.
Adjacent sequences: A059785 A059786 A059787 this_sequence A059789 A059790 A059791
Sequence in context: A120460 A127459 A075579 this_sequence A077171 A065384 A126108
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Feb 22 2001
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