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 A293399 Numbers k such that (68*10^k - 11)/3 is prime. 0
 0, 1, 4, 6, 9, 20, 57, 64, 88, 196, 265, 421, 620, 654, 729, 1587, 4863, 6628, 12358, 23773, 68798 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For k > 0, numbers such that the digits 22 followed by k-1 occurrences of the digit 6 followed by the digit 3 is prime (see Example section). a(22) > 10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 226w3 EXAMPLE 1 is in this sequence because (68*10^1 - 11)/3 = 223 is prime. Initial terms and primes associated: a(1) = 0, 19; a(2) = 1, 223; a(3) = 4, 226663; a(4) = 6, 22666663; a(5) = 9, 22666666663; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(68*10^3 - 11)/3] &] PROG (PARI) isok(k) = isprime((68*10^k - 11)/3); \\ Altug Alkan, Oct 08 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A152002 A171127 A098485 * A120712 A115698 A039566 Adjacent sequences:  A293396 A293397 A293398 * A293400 A293401 A293402 KEYWORD nonn,more,hard,changed AUTHOR Robert Price, Oct 08 2017 STATUS approved

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Last modified January 17 19:58 EST 2019. Contains 319251 sequences. (Running on oeis4.)