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 A110782 #11 Nov 14 2021 12:33:17 %S A110782 11,3,777,999,11,33333333,777777777777777777777, %T A110782 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999, %U A110782 1111111111111111111111111 %N A110782 Copies of 1,3,7 and 9 cyclically such that every partial concatenation is a prime. %e A110782 11, 113, 113777, 113777999, ... are all prime. %Y A110782 Cf. A110774, A110775, A110776, A110777, A110778, A110780, A110781, A110783. %K A110782 base,nonn %O A110782 1,1 %A A110782 _Amarnath Murthy_, Aug 12 2005 %E A110782 More terms from _Joshua Zucker_, Jan 11 2006 %E A110782 The next term is 726 3's and is too large to include.