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A125524
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Republican primes: primes such that the right half of the prime is prime and the left half is not.
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4
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13, 17, 43, 47, 67, 83, 97, 103, 107, 113, 127, 137, 157, 163, 167, 173, 193, 197, 433, 443, 457, 463, 467, 487, 607, 613, 617, 643, 647, 653, 673, 677, 683, 823, 827, 853, 857, 863, 877, 883, 887, 907, 937, 947, 953, 967, 977, 983, 997, 1013, 1019, 1031
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OFFSET
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2,1
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COMMENTS
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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.
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LINKS
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EXAMPLE
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The right half of 13 is 3, which is prime. The left half is 1, which is not prime.
The right half of 113 is 3, which is prime. The left half is 1, which is not prime.
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PROG
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(PARI) /* Political primes, republican 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", ") ) ) }
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CROSSREFS
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KEYWORD
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base,easy,nonn
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AUTHOR
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STATUS
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approved
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