Search: id:A125525
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%I A125525
%S A125525 2,3,5,7,23,37,53,73,223,227,233,257,263,277,283,293,307,313,317,337,
%T A125525 347,353,367,373,383,397,503,523,547,557,563,577,587,593,727,733,743,
%U A125525 757,773,787,797,1103,1117,1123,1129,1153,1171,1303,1307,1319,1361,1367
%N A125525 Centrist primes. Primes such that both the right half and the left half 
               of the prime is prime.
%C A125525 If the length of n > 9 is odd then the central number is not used in 
               the calculation. So neither the left half nor the right half will 
               contain the central digit. If the length of n is even, then all numbers 
               are used. My guess is these numbers are infinite.
%F A125525 Half n > 9 is the floor of the length of n divided by 2. For n <= 9 half 
               n is 1.
%e A125525 The right half of 23 is 2 which is prime. The left half is 3 which is 
               also prime so 23 is a centrist prime.
%o A125525 (PARI) \Political primes, Centrist case. rep(n) = { local(x,ln,y,lp,rp); 
               forprime(x=2,n, y=Str(x); if(x > 9, ln=floor(length(y)/2), ln=1); 
               lp = eval(left(y,ln)); rp = eval(right(y,ln)); if(isprime(lp)&& isprime(rp),
               print1(x",") ) ) }
%Y A125525 Sequence in context: A154761 A074491 A154385 this_sequence A019546 A104179 
               A096148
%Y A125525 Adjacent sequences: A125522 A125523 A125524 this_sequence A125526 A125527 
               A125528
%K A125525 base,easy,nonn
%O A125525 2,1
%A A125525 Cino Hilliard (hillcino368(AT)hotmail.com), Jan 22 2007

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