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 A165243 Primes obtained from other primes by pre-concatenating with 2. 7
 23, 211, 223, 229, 241, 271, 283, 2113, 2131, 2137, 2179, 2239, 2251, 2269, 2281, 2293, 2311, 2347, 2383, 2389, 2467, 2503, 2521, 2557, 2593, 2617, 2647, 2659, 2677, 2683, 2719, 2797, 2857, 2887, 2953, 2971, 21013, 21019, 21031, 21061, 21163, 21187 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..42. EXAMPLE The prime 2971 is from the prime 971 by pre-concatenating with 2. MATHEMATICA Select[Map[FromDigits, Map[Join[{2}, #] &, IntegerDigits[Prime[Range[200]]]]], PrimeQ[#] &] (* Robert Price, Mar 31 2019 *) PROG (PARI) terms(n) = my(i=0, cc=[]); forprime(p=1, , cc=eval(concat("2", Str(p))); if(ispseudoprime(cc), print1(cc, ", "); i++); if(i==n, break)) /* Print initial 40 terms as follows: */ terms(40) \\ Felix Fröhlich, Mar 31 2019 CROSSREFS Cf. A000040 Sequence in context: A322287 A327918 A327919 * A142374 A171342 A112747 Adjacent sequences: A165240 A165241 A165242 * A165244 A165245 A165246 KEYWORD base,nonn AUTHOR Parthasarathy Nambi, Sep 09 2009 EXTENSIONS 2269 inserted by R. J. Mathar, Sep 21 2009 STATUS approved

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Last modified July 19 22:34 EDT 2024. Contains 374441 sequences. (Running on oeis4.)