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 A372056 #18 Jun 20 2024 02:43:02 %S A372056 13,23,-1,43,53,-1,73,83,-1,103,113,-1,1333333333333333,1433,-1,163, %T A372056 173,-1,193,20333,-1,223,233,-1,2533333333,263,-1,283,293,-1,313, %U A372056 323333,-1,3433,353,-1,373,383,-1 %N A372056 Smallest prime obtained by appending one or more 3's to n, or -1 if no such prime exists. %C A372056 Next term is 40 followed by 483 3's and is too large to display here (see the b-file). %H A372056 Toshitaka Suzuki, <a href="/A372056/b372056.txt">Table of n, a(n) for n = 1..409</a> %e A372056 For n = 13, a(13) = 1333333333333333 is a prime (but 133,1333,13333 etc. are not primes). %Y A372056 See A112394 for another version. %Y A372056 Cf. A030431, A090584, A112386, A113076. %K A372056 base,sign %O A372056 1,1 %A A372056 _Toshitaka Suzuki_, Mar 30 2024 %E A372056 Edited by _N. J. A. Sloane_, Apr 24 2024