login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A294916 Numbers k such that (10^k + 191)/3 is prime. 0

%I #10 Jan 17 2019 13:44:10

%S 1,2,3,6,7,13,18,33,39,126,154,168,213,4150,4153,5658,6394,21993,

%T 29674,38936,47095,94096,135174,139398

%N Numbers k such that (10^k + 191)/3 is prime.

%C For k > 1, numbers such that k-2 occurrences of the digit 3 followed by the digits 97 is prime (see Example section).

%C a(25) > 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/primedifficulty.txt">Search for 3w97</a>

%e 2 is in this sequence because (10^2 + 191)/3 = 97 is prime.

%e Initial terms and primes associated:

%e a(1) = 1, 67;

%e a(2) = 2, 97;

%e a(3) = 3, 397;

%e a(4) = 6, 333397;

%e a(5) = 7, 3333397; etc.

%t Select[Range[0, 100000], PrimeQ[(10^# + 191)/3] &]

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

%K nonn,more,hard

%O 1,2

%A _Robert Price_, Nov 10 2017

%E a(23)-a(24) from _Robert Price_, Feb 14 2018

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 29 09:59 EDT 2024. Contains 371268 sequences. (Running on oeis4.)