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A069686
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Primes whose internal digits form a prime.
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12
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127, 131, 137, 139, 151, 157, 173, 179, 223, 227, 229, 233, 239, 251, 257, 271, 277, 331, 337, 353, 359, 373, 379, 421, 431, 433, 439, 457, 479, 521, 523, 557, 571, 577, 631, 653, 659, 673, 677, 727, 733, 739, 751, 757, 773, 821, 823, 827, 829, 839, 853
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OFFSET
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1,1
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COMMENTS
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Primes that remain prime upon deleting the first and last digits.
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LINKS
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MATHEMATICA
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Select[Range[100, 853], PrimeQ[#] && PrimeQ[FromDigits[Rest[Most[IntegerDigits[#]]]]] &] (* T. D. Noe, Apr 05 2013 *)
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PROG
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(PARI) {indigs(n)=local(j, a, d); n=n\10; j=1; a=0; while(n>10, d=divrem(n, 10); n=d[1]; a=a+j*d[2]; j=10*j); a}
forprime(p=1, 855, if(isprime(indigs(p)), print1(p, ", "))) \\ Klaus Brockhaus, Nov 06 2002
(Python)
from sympy import isprime
for p in filter(isprime, range(100, 855)):
if isprime(int(str(p)[1:-1])): print(p) # Jason Yuen, Mar 28 2024
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CROSSREFS
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KEYWORD
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base,nonn,easy,changed
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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