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 A032711 Numbers k such that the concatenation '2',k,'3' is prime. 7
 2, 3, 6, 8, 9, 11, 14, 15, 20, 21, 24, 27, 29, 33, 38, 39, 42, 47, 50, 54, 59, 63, 66, 68, 69, 71, 75, 80, 83, 84, 90, 95, 96, 101, 102, 114, 116, 119, 128, 131, 132, 138, 143, 149, 150, 152, 156, 161, 167, 168, 171, 177, 180, 186, 189, 194, 200, 201, 206, 207, 209 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS This sequence is infinite, a consequence of the Prime Number Theorem in arithmetic progressions. - Charles R Greathouse IV, Sep 26 2012 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 EXAMPLE 8 and 21 are in the sequence because 283 and 2213 are primes. MATHEMATICA v={}; Do[If[PrimeQ[FromDigits[Join[{2}, IntegerDigits[n], {3}]]], v=Append[v, n]], {n, 260}]; v (* *) - Farideh Firoozbakht, Jun 15 2003 Select[Range[210], PrimeQ[FromDigits[Join[{2}, IntegerDigits[#], {3}]]]&] (* Harvey P. Dale, May 02 2012 *) PROG (PARI) for( n=1, 300, isprime(eval(Str(2, n, 3))) & print1(n", ")) \\ M. F. Hasler, Mar 18 2008 CROSSREFS Cf. A083677, A083966, A083969, A092117. Sequence in context: A013952 A105042 A092114 * A135768 A287659 A047244 Adjacent sequences:  A032708 A032709 A032710 * A032712 A032713 A032714 KEYWORD nonn,base AUTHOR Patrick De Geest, May 15 1998 EXTENSIONS Merged with data from duplicate entry A092114. - M. F. Hasler, Mar 18 2008 STATUS approved

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Last modified January 29 01:19 EST 2022. Contains 350670 sequences. (Running on oeis4.)