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!)
A295326 Numbers k such that (182*10^k + 43)/9 is prime. 0

%I #13 Feb 01 2020 22:41:26

%S 2,6,14,17,27,86,104,107,132,300,374,405,497,1179,1994,4274,5252,

%T 17939,39534,82898,85017,106083

%N Numbers k such that (182*10^k + 43)/9 is prime.

%C For k > 1, numbers such that the digits 20 followed by k-1 occurrences of the digit 2 followed by the digit 7 is prime (see Example section).

%C a(23) > 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 202w7</a>.

%e 2 is in this sequence because (182*10^2 + 43)/9 = 2027 is prime.

%e Initial terms and primes associated:

%e a(1) = 2, 2027;

%e a(2) = 6, 20222227;

%e a(3) = 14, 2022222222222227;

%e a(4) = 17, 2022222222222222227;

%e a(5) = 27, 20222222222222222222222222227; etc.

%t Select[Range[0, 100000], PrimeQ[(182*10^# + 43)/9] &]

%o (PARI) isok(k) = isprime((182*10^k + 43)/9); \\ _Michel Marcus_, Nov 20 2017

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

%K nonn,more,hard

%O 1,1

%A _Robert Price_, Nov 19 2017

%E a(22) from _Robert Price_, Feb 01 2020

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 22:15 EDT 2024. Contains 371282 sequences. (Running on oeis4.)