Search: id:A030461
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%I A030461
%S A030461 23,3137,8389,151157,157163,167173,199211,233239,251257,257263,
%T A030461 263269,271277,331337,353359,373379,433439,467479,509521,523541,
%U A030461 541547,601607,653659,661673,677683,727733,941947,971977,10131019
%N A030461 Primes that are concatenations of two consecutive primes.
%C A030461 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
%H A030461 Zak Seidov, <a href="b030461.txt">Table of n, a(n) for n=1..1000</a>
%e A030461 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
%p A030461 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)
%o A030461 (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)
%Y A030461 Cf. A030459.
%Y A030461 Sequence in context: A132937 A068655 A088385 this_sequence A152521 A136363 
               A134798
%Y A030461 Adjacent sequences: A030458 A030459 A030460 this_sequence A030462 A030463 
               A030464
%K A030461 nonn,base
%O A030461 1,1
%A A030461 Patrick De Geest (pdg(AT)worldofnumbers.com)
%E A030461 Edited by N. J. A. Sloane, Apr 19 2009 at the suggestion of Zak Seidov

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