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 A254519 #9 Feb 13 2015 09:33:11 %S A254519 91,949,8911,97567,997633,9959413,99971821,999271891,9999326731, %T A254519 99997244929,999989423051,9999899578441,99999695823301, %U A254519 999999050050321,9999997295187859,99999997019370001 %N A254519 Largest n-digit pseudoprime to base 3. %o A254519 (PARI) for(n=2, 20, k=10^n; while(ispseudoprime(k) || Mod(3, k)^(k-1)!=1, k--); print1(k, ", ")) %Y A254519 Cf. A005935, A067845. %K A254519 nonn,hard,base,more %O A254519 2,1 %A A254519 _Felix Fröhlich_, Jan 31 2015