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 A278611 #18 Oct 11 2019 08:39:50 %S A278611 2,6,34 %N A278611 Bases b > 1 that set a new record for the size of the smallest base-b Wieferich prime. %C A278611 Numbers n such that A039951(n) reaches a new record value. %C A278611 a(1) = 2. Thereafter smallest number x that occurs later in column 1 of A244249 than any y with 1 < y < x. %C A278611 Let b(n) be the sequence of corresponding smallest Wieferich primes. b(1)-b(3) are 1093, 66161 and 46145917691, respectively (cf. A307220). %C A278611 No term is a perfect power, since then its smallest Wieferich prime is at most the size of the smallest Wieferich prime of the base that is raised to a power. %C A278611 a(4) is either 47, 72 or 139, depending on which of those bases is the smallest where any Wieferich prime exists. The smallest base-139 Wieferich prime is 1822333408543 and any Wieferich primes in bases 47 and 72 are larger than 1.07*10^14 (cf. Fischer). %H A278611 R. Fischer, <a href="http://www.fermatquotient.com/FermatQuotienten/FermQ_Sort.txt">Thema: Fermatquotient B^(P-1) == 1 (mod P^2)</a> %e A278611 a(2) = 6, since the smallest base-6 Wieferich prime is 66161 and that prime is the second term with a record value in A039951. %o A278611 (PARI) smallest_w_prime(n) = forprime(p=1, , if(Mod(n, p^2)^(p-1)==1, return(p))) %o A278611 my(r=0, b=2); while(1, if(smallest_w_prime(b) > r, print1(b, ", "); r=smallest_w_prime(b)); b++) %Y A278611 Cf. A039951, A244249, A307220. %K A278611 nonn,hard,more,bref %O A278611 1,1 %A A278611 _Felix Fröhlich_, Nov 23 2016