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 A276672 Numbers n such that (19*10^n + 101) / 3 is prime. 0
 1, 3, 4, 9, 10, 12, 13, 16, 20, 37, 57, 66, 106, 116, 127, 355, 396, 547, 2289, 3777, 4500, 7821, 15663, 22746, 25978, 30434, 39682, 119716, 133390, 145093 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS For n>1, numbers such that the digit 6 followed by n-2 occurrences of the digit 3 followed by the digits 67 is prime (see Example section). a(31) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 63w67. EXAMPLE 3 is in this sequence because (19*10^3 + 101) / 3 = 6367 is prime. Initial terms and primes associated: a(1) = 1, 97; a(2) = 3, 6367; a(3) = 4, 63367; a(4) = 9, 6333333367; a(5) = 10, 63333333367, etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(19*10^# + 101) / 3] &] PROG (MAGMA) [n: n in [0..400] |IsPrime((19*10^n + 101) div 3)]; // Vincenzo Librandi, Sep 13 2016 (PARI) is(n)=ispseudoprime((19*10^n + 101)/3) \\ Charles R Greathouse IV, Jun 13 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A010376 A010388 A283973 * A010400 A010439 A005836 Adjacent sequences:  A276669 A276670 A276671 * A276673 A276674 A276675 KEYWORD nonn,more AUTHOR Robert Price, Sep 12 2016 EXTENSIONS a(28)-a(30) from Robert Price, Sep 01 2019 STATUS approved

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Last modified May 31 13:01 EDT 2020. Contains 334748 sequences. (Running on oeis4.)