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Search: id:A030461
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| A030461 |
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Primes that are concatenations of two consecutive primes. |
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+0
3
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| 23, 3137, 8389, 151157, 157163, 167173, 199211, 233239, 251257, 257263, 263269, 271277, 331337, 353359, 373379, 433439, 467479, 509521, 523541, 541547, 601607, 653659, 661673, 677683, 727733, 941947, 971977, 10131019
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Any term in the sequence (apart from the first) must be a concatenation of consecutive primes differing by a multiple of 6. - Francis J McDonnell (francis(AT)polytopia.freeserve.co.uk), Jun 26 2005
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LINKS
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Zak Seidov, Table of n, a(n) for n=1..1000
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EXAMPLE
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a(2) is 3137 because 31 and 37 are consecutive primes and after concatenation 3137 is also prime. - Enoch Haga (Enokh(AT)comcast.net), Sep 30 2007
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MAPLE
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conc:=proc(a, b) local bb: bb:=convert(b, base, 10): 10^nops(bb)*a+b end: p:=proc(n) local w: w:=conc(ithprime(n), ithprime(n+1)): if isprime(w)=true then w else fi end: seq(p(n), n=1..250); (Emeric Deutsch)
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PROGRAM
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(PARI) {digits(n) = if(n==0, [0], u=[]; while(n>0, d=divrem(n, 10); n=d[1]; u=concat(d[2], u)); u)} {m=1185; p=2; while(p<m, q=nextprime(p+1); s=""; v=digits(p); for(j=1, length(v), s=concat(s, v[j])); v=digits(q); for(j=1, length(v), s=concat(s, v[j])); if(isprime(k=eval(s)), print1(k, ", ")); p=q)} (Klaus Brockhaus)
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CROSSREFS
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Cf. A030459.
Sequence in context: A132937 A068655 A088385 this_sequence A152521 A136363 A134798
Adjacent sequences: A030458 A030459 A030460 this_sequence A030462 A030463 A030464
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KEYWORD
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nonn,base
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AUTHOR
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Patrick De Geest (pdg(AT)worldofnumbers.com)
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EXTENSIONS
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Edited by N. J. A. Sloane, Apr 19 2009 at the suggestion of Zak Seidov
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