Search: id:A125523
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%I A125523
%S A125523 29,31,59,71,79,211,229,239,241,251,269,271,281,311,331,349,359,379,389,
%T A125523 509,521,541,569,571,599,701,709,719,739,751,761,769,1109,1151,1163,
%U A125523 1181,1187,1193,1301,1321,1327,1381,1399,1709,1721,1733,1777,1787,1901
%N A125523 Democratic primes. Primes such that the left half of the prime is prime 
               and the right half is not.
%C A125523 If the length of n 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.
%F A125523 Half n is the floor of the length of n divided by 2.
%e A125523 The left half of 29 is 2 which is prime. The right half is 9 which is 
               not prime.
%e A125523 The left half of 211 is 2 which is prime. The right half is 1 which is 
               not prime.
%o A125523 (PARI) \Political primes, democratic case. dem(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 A125523 Sequence in context: A104071 A132240 A132243 this_sequence A156976 A157681 
               A077286
%Y A125523 Adjacent sequences: A125520 A125521 A125522 this_sequence A125524 A125525 
               A125526
%K A125523 base,easy,nonn
%O A125523 2,1
%A A125523 Cino Hilliard (hillcino368(AT)hotmail.com), Jan 22 2007

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