The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A256570 Numbers k such that 3*R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length n. 0

%I

%S 1,2,4,5,11,16,22,24,110,232,557,566,888,1946,2610,3302,10214,41756,

%T 89160,120782

%N Numbers k such that 3*R_k + 10 is prime, where R_k = 11...1 is the repunit (A002275) of length n.

%C Also, numbers k such that (10^k + 29)/3 is prime.

%C Terms from Kamada data. Note Kamada does not recognize k=1 as 13 is a degenerate case of form AAA..ABA.

%C a(21) > 2.5*10^5.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/aaaba.htm">Near-repdigit numbers of the form AA...AABA</a>.

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/3/33343.htm#prime">Prime numbers of the form 33...3343</a>.

%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.

%e For k=4, 3*R_4 + 10 = 3333 + 10 = 3343 which is prime.

%t Select[Range[0, 250000], PrimeQ[(10^# + 29)/3] &]

%o (MAGMA) [n: n in [0..400] | IsPrime((10^n+29) div 3)]; // _Vincenzo Librandi_, Apr 11 2015

%Y Cf. A002275.

%K more,hard,nonn

%O 1,2

%A _Robert Price_, Apr 10 2015

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

Last modified September 27 10:35 EDT 2020. Contains 337380 sequences. (Running on oeis4.)