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 A293757 Numbers k such that (10^k - 97)/3 is prime. 0
 4, 5, 7, 13, 16, 22, 30, 56, 78, 80, 90, 194, 316, 1796, 2004, 3856, 5226, 6737, 10841, 43638, 50467, 85666 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k > 1, numbers k such that k-2 occurrences of the digit 3 followed by the digits 01 is prime (see Example section). a(23) > 2*10^5. LINKS Table of n, a(n) for n=1..22. Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 3w01. EXAMPLE 4 is in this sequence because (10^4 - 97)/3 = 3301 is prime. Initial terms and associated primes: a(1) = 4, 3301; a(2) = 5, 33301; a(3) = 7, 3333301; a(4) = 13, 3333333333301; a(5) = 16, 3333333333333301; etc. MATHEMATICA Select[Range[2, 100000], PrimeQ[(10^# - 97)/3] &] PROG (Magma) [n: n in [1..400] |IsPrime((10^n-97) div 3)]; // Vincenzo Librandi, Oct 16 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A048224 A064237 A139373 * A275273 A069575 A250182 Adjacent sequences: A293754 A293755 A293756 * A293758 A293759 A293760 KEYWORD nonn,more,hard AUTHOR Robert Price, Oct 15 2017 EXTENSIONS Example and Link corrected by Robert Price, Nov 22 2017 STATUS approved

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Last modified August 5 11:26 EDT 2024. Contains 374950 sequences. (Running on oeis4.)