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 A268352 #4 Feb 07 2016 20:18:44 %S A268352 3511,1006003,3511,20771,534851,491531,1093,11,487 %N A268352 Second base-n Wieferich prime, i.e., second smallest prime p such that n^(p-1) == 1 (mod p^2). %C A268352 Column 2 of table T(n, k) of k-th base-n Wieferich prime for n > 1 (that table is not yet in the OEIS as a sequence). %C A268352 a(11) is unknown, but must be larger than 1.202*10^13 if it exists (cf. Fischer). %H A268352 R. Fischer, <a href="http://www.fermatquotient.com/FermatQuotienten/FermQ_Sort.txt">Thema: Fermatquotient B^(P-1) == 1 (mod P^2)</a> %e A268352 a(3) = 1006003, because 1006003 is the second smallest prime p satisfying 3^(p-1) == 1 (mod p^2) (see A014127). %o A268352 (PARI) a(n) = my(i=0); forprime(p=1, , if(Mod(n, p^2)^(p-1)==1, if(i > 0, return(p), i++))) %Y A268352 Cf. A039951, A178871. %K A268352 nonn,hard,more %O A268352 2,1 %A A268352 _Felix Fröhlich_, Feb 02 2016