This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A077783 #51 Sep 05 2023 09:38:06
%S A077783 3,15,91,231,1363,2497,4963,5379,12397,26395,120253,200145
%N A077783 Numbers k such that (10^k-1)/9 + 4*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
%C A077783 Prime versus probable prime status and proofs are given in the author's table.
%C A077783 a(13) > 200466. - __Robert Price_, Sep 05 2023
%D A077783 C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
%H A077783 Patrick De Geest, World!Of Numbers, <a href="http://www.worldofnumbers.com/wing.htm#pwp151">Palindromic Wing Primes (PWP's)</a>
%H A077783 Makoto Kamada, <a href="https://stdkmd.net/nrr/1/11511.htm#prime">Prime numbers of the form 11...11511...11</a>
%H A077783 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A077783 a(n) = 2*A107125(n) + 1.
%e A077783 15 is a term because (10^15 - 1)/9 + 4*10^7 = 111111151111111.
%t A077783 Do[ If[ PrimeQ[(10^n + 36*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 26400, 2}] (* _Robert G. Wilson v_, Dec 16 2005 *)
%o A077783 (Magma) [n: n in [3..2000 by 2] | IsPrime((10^n+36*10^(n div 2)-1) div 9)]; // _Vincenzo Librandi_, Oct 13 2015
%Y A077783 Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
%K A077783 more,nonn,base
%O A077783 1,1
%A A077783 _Patrick De Geest_, Nov 16 2002
%E A077783 a(11) from _Robert Price_, Oct 12 2015
%E A077783 Name edited by _Jon E. Schoenfield_, Oct 13 2015
%E A077783 a(12) from _Robert Price_, Sep 05 2023