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 A281276 Numbers k such that (2*10^k + 457)/9 is prime. 0
 1, 2, 4, 5, 7, 8, 11, 13, 20, 22, 38, 47, 76, 269, 299, 527, 724, 1214, 2243, 2327, 12635, 15064, 28921, 34303, 49117, 58151, 89279, 199283 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For k>2, numbers such that k-2 occurrences of the digit 2 followed by the digits 73 is prime (see Example section). a(29) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 2w73. EXAMPLE 2 is in this sequence because (2*10^2 + 457) / 9 = 73 is prime. Initial terms and primes associated: a(1) = 1, 53; a(2) = 2, 73; a(3) = 4, 2273; a(4) = 5, 22273; a(5) = 7, 2222273; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(2*10^# + 457) / 9] &] CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A001606 A014554 A114147 * A025516 A191174 A261188 Adjacent sequences:  A281273 A281274 A281275 * A281277 A281278 A281279 KEYWORD nonn,more,hard AUTHOR Robert Price, Jan 18 2017 EXTENSIONS a(28) from Robert Price, Jan 08 2018 STATUS approved

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Last modified December 5 20:39 EST 2021. Contains 349558 sequences. (Running on oeis4.)