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 A077779 #42 Mar 26 2020 11:13:49
%S A077779 3,5,39,195,19637
%N A077779 Numbers k such that (10^k - 1)/9 + 2*10^floor(k/2) is a palindromic wing prime (a.k.a. near-repdigit palindromic prime).
%C A077779 Prime versus probable prime status and proofs are given in the author's table.
%C A077779 a(6) > 2*10^5. - _Robert Price_, Apr 02 2016
%C A077779 The number k = 1 would also correspond to a prime, 3, but not "near-repdigit" or "wing" in a strict sense. - _M. F. Hasler_, Feb 09 2020
%D A077779 C. Caldwell and H. Dubner, "Journal of Recreational Mathematics", Volume 28, No. 1, 1996-97, pp. 1-9.
%H A077779 Patrick De Geest, World!Of Numbers, <a href="http://www.worldofnumbers.com/wing.htm#pwp131">Palindromic Wing Primes (PWP's)</a>
%H A077779 Makoto Kamada, <a href="https://stdkmd.net/nrr/1/11311.htm#prime">Prime numbers of the form 11...11311...11</a>
%H A077779 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A077779 a(n) = 2*A107123(n+1) + 1.
%e A077779 5 is a term because (10^5 - 1)/9 + 2*10^2 = 11311.
%t A077779 Do[ If[ PrimeQ[(10^n + 18*10^Floor[n/2] - 1)/9], Print[n]], {n, 3, 20000, 2}] (* _Robert G. Wilson v_, Dec 16 2005 *)
%Y A077779 Cf. A004023, A077775-A077798, A107123-A107127, A107648, A107649, A115073, A183174-A183187.
%Y A077779 See A332113 for the (prime and composite) near-repunit palindromes 1..131..1.
%K A077779 nonn,base,more
%O A077779 1,1
%A A077779 _Patrick De Geest_, Nov 16 2002
%E A077779 Name corrected by _Jon E. Schoenfield_, Oct 31 2018