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A179826
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Primes that can be obtained from composite numbers by interchanging the first and last digits.
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2
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41, 61, 2, 3, 23, 43, 53, 83, 5, 7, 47, 67, 19, 29, 59, 89, 401, 601, 11, 211, 811, 911, 421, 521, 821, 31, 331, 431, 631, 41, 241, 541, 641, 251, 61, 461, 661, 71, 271, 571, 281, 881, 491, 691, 2, 3, 103, 503, 13, 613, 23, 223, 523, 823, 233, 433, 43, 443, 643, 53
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OFFSET
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1,1
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COMMENTS
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The composite number must contain at least two digits.
Primes may be repeated; the reverted A002808(j) are investigated along increasing j and their trailing zeros become leading zeros and are dropped. [R. J. Mathar, Jul 30 2010]
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LINKS
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EXAMPLE
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41 is a prime from the composite number 14 by interchanging the first and last digit. 47 is a prime from the composite number 74 by interchanging the first and last digit.
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MATHEMATICA
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nonpr=Complement[Range[10, 1000], Prime[Range[PrimePi[1000]]]];
swtch[n_]:=Module[{idn=IntegerDigits[n], f, l, m}, f=First[idn]; l=Last[idn]; m=Most[Rest[idn]]; FromDigits[Join[{l}, m, {f}]]]
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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