Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #43 Dec 06 2023 18:25:14
%S 9,11,17,23,2489,3371,4019,29315,30237,40665,101661,150125
%N Numbers k such that 7*(10^k - 1)/9 - 10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
%C Prime versus probable prime status and proofs are given in the author's table.
%D C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
%H Patrick De Geest, World!Of Numbers, <a href="http://www.worldofnumbers.com/wing.htm#pwp767">Palindromic Wing Primes (PWP's)</a>
%H Makoto Kamada, <a href="https://stdkmd.net/nrr/7/77677.htm#prime">Prime numbers of the form 77...77677...77</a>
%H <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F a(n) = 2*A183181(n) + 1.
%e 11 is a term because 7*(10^11 - 1)/9 - 10^5 = 77777677777.
%t Do[ If[ PrimeQ[(7*10^n - 9*10^Floor[n/2] - 7)/9], Print[n]], {n, 3, 30300, 2}] (* _Robert G. Wilson v_, Dec 16 2005 *)
%Y Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
%K more,nonn,base
%O 1,1
%A _Patrick De Geest_, Nov 16 2002
%E Name corrected by _Jon E. Schoenfield_, Oct 31 2018
%E a(10) from _Robert Price_, Oct 07 2023
%E a(11) from _Robert Price_, Oct 17 2023
%E a(12) from _Robert Price_, Dec 06 2023