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 A309808 Primes formed by concatenating k and 2k+1. 5
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Primes in A309809. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(3)=613 is the concatenation of 6 and 2*6+1=13 and is prime. MAPLE select(isprime, [seq(n*10^(1+ilog10(2*n+1))+2*n+1, n=1..200)]); PROG (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 CROSSREFS Cf. A030458, A309809. Sequence in context: A098265 A195540 A262475 * A201809 A129541 A302858 Adjacent sequences: A309805 A309806 A309807 * A309809 A309810 A309811 KEYWORD nonn,base AUTHOR J. M. Bergot and Robert Israel, Aug 17 2019 STATUS approved

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Last modified August 10 02:46 EDT 2024. Contains 375044 sequences. (Running on oeis4.)