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 A093167 #29 Jul 08 2021 06:20:13 %S A093167 7,227,222222227,222222222222227,2222222222222222222222222227, %T A093167 2222222222222222222222222222222222222222222222222222222222222227 %N A093167 Primes of the form 20*R_k + 7, where R_k is the repunit (A002275) of length k. %H A093167 Makoto Kamada, <a href="https://stdkmd.net/nrr/2/22227.htm#prime">Prime numbers of the form 22...227</a>. %H A093167 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a> %t A093167 Select[FromDigits /@ NestList["2" <> # &, "7", 10^3], PrimeQ] (* _Mikk Heidemaa_, Nov 18 2015 *) %o A093167 (PARI) list(lim)=for(i=0,lim,m=20*(10^i-1)/9 + 7;if(isprime(m),print1(m," ,"))) \\ _Anders Hellström_, Nov 18 2015 %Y A093167 Cf. A002275, A056677 (corresponding k and count of digits 2 in a(n)), A099409. %K A093167 nonn,base %O A093167 1,1 %A A093167 _Rick L. Shepherd_, Mar 26 2004