A274214 - OEIS

%I #16 May 02 2024 04:26:59

%S 0,1,2,4,6,9,11,14,16,26,54,74,111,130,152,253,345,607,686,1590,2711,

%T 5462,7021,8681,11044,18132,24072,25211,44332,52792,85881

%N Numbers k such that 4*10^k + 63 is prime.

%C For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 63 is prime (see Example section).

%C a(32) > 2*10^5.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 40w63</a>.

%e 4 is in this sequence because 4*10^4 + 63 = 40063 is prime.

%e Initial terms and associated primes:

%e a(1) = 0, 67;

%e a(2) = 1, 103;

%e a(3) = 2, 463;

%e a(4) = 4, 40063;

%e a(5) = 6, 4000063, etc.

%t Select[Range[0, 100000], PrimeQ[4*10^# + 63] &]

%o (PARI) is(n)=ispseudoprime(4*10^n + 63) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.

%K nonn,more

%O 1,3

%A _Robert Price_, Jun 13 2016