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 A110776 #5 Nov 14 2021 12:36:51 %S A110776 11,777,11,777777,111111111,7777777777777777777777777,111111111,777 %N A110776 Copies of 1 and 7 alternately such that every partial concatenation is a prime. %e A110776 11, 11777, 1177711, ... are all prime. %Y A110776 Cf. A110774, A110775, A110777, A110778, A112534, A110780, A110781, A110782, A110783, A110788, A110789. %K A110776 base,nonn %O A110776 1,1 %A A110776 _Amarnath Murthy_, Aug 12 2005 %E A110776 Corrected and extended by _Joshua Zucker_, Jan 11 2006 %E A110776 The next term has 762 1's and is too large to include.