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A309808
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Primes formed by concatenating k and 2k+1.
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5
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13, 37, 613, 919, 1021, 1123, 1327, 1429, 1531, 2143, 2347, 2551, 2857, 3061, 3163, 3469, 3571, 3673, 3877, 4591, 4999, 50101, 56113, 59119, 63127, 70141, 71143, 74149, 78157, 79159, 81163, 88177, 91183, 93187, 95191, 101203, 105211, 106213, 108217, 110221, 113227, 114229
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OFFSET
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1,1
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COMMENTS
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LINKS
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EXAMPLE
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a(3)=613 is the concatenation of 6 and 2*6+1=13 and is prime.
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MAPLE
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select(isprime, [seq(n*10^(1+ilog10(2*n+1))+2*n+1, n=1..200)]);
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PROG
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(Magma) [a:m in [1..130]|IsPrime(a) where a is 10^(#Intseq(2*m+1))*m+2*m+1]; // Marius A. Burtea, Aug 18 2019
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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