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 A077791 #30 Aug 03 2024 18:59:11
%S A077791 3,9,13,15,769,1333,1351,6331,262041
%N A077791 Numbers k such that (10^k - 1)/9 + 7*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
%C A077791 Prime versus probable prime status and proofs are given in the author's table.
%D A077791 C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
%H A077791 Patrick De Geest, World!Of Numbers, <a href="http://www.worldofnumbers.com/wing.htm#pwp181">Palindromic Wing Primes (PWP's)</a>
%H A077791 Makoto Kamada, <a href="https://stdkmd.net/nrr/1/11811.htm#prime">Prime numbers of the form 11...11811...11</a>
%H A077791 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A077791 a(n) = 2*A107648(n) + 1.
%e A077791 13 is a term (10^13 - 1)/9 + 7*10^6 = 1111118111111.
%t A077791 Do[ If[ PrimeQ[(10^n + 63*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 6400, 2}] (* _Robert G. Wilson v_, Dec 16 2005 *)
%Y A077791 Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
%K A077791 more,nonn,base
%O A077791 1,1
%A A077791 _Patrick De Geest_, Nov 16 2002
%E A077791 Name corrected by _Jon E. Schoenfield_, Oct 31 2018
%E A077791 a(9) from _Robert Price_, Aug 03 2024