cp's OEIS Frontend

A270339 Numbers k such that (11*10^k + 19)/3 is prime.

%I A270339 #15 Jul 25 2024 14:26:35
%S A270339 1,2,3,9,17,18,20,24,29,36,48,114,126,135,153,170,241,363,483,579,681,
%T A270339 948,2483,2798,3081,5137,5640,6890,7080,12600,16929,24253,24793,35546,
%U A270339 52956,69645,133831,206688
%N A270339 Numbers k such that (11*10^k + 19)/3 is prime.
%C A270339 For k > 1, numbers k such that the digit 3 followed by k-2 occurrences of the digit 6 followed by the digits 73 is prime (see Example section).
%C A270339 a(39) > 3*10^5.
%H A270339 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 36w73</a>.
%e A270339 3 is in this sequence because (11*10^3 + 19)/3 = 3673 is prime.
%e A270339 Initial terms and associated primes:
%e A270339 a(1) = 1, 43;
%e A270339 a(2) = 2, 373;
%e A270339 a(3) = 3, 3673;
%e A270339 a(4) = 9, 3666666673;
%e A270339 a(5) = 17, 366666666666666673, etc.
%t A270339 Select[Range[0, 100000], PrimeQ[(11*10^# + 19)/3] &]
%o A270339 (PARI) is(n)=isprime((11*10^n + 19)/3) \\ _Charles R Greathouse IV_, Mar 16 2016
%Y A270339 Cf. A056654, A268448, A269303.
%K A270339 nonn,more
%O A270339 1,2
%A A270339 _Robert Price_, Mar 15 2016
%E A270339 a(37) from _Robert Price_, Sep 16 2018
%E A270339 a(38) from _Robert Price_, Jul 25 2024