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 A339639 #7 Dec 21 2020 07:17:34 %S A339639 3,6,20,35,110,78,493,114,736,783,961,518,2542,2752,2820,3392,1062, %T A339639 5124,1139,4047,8322,5372,5727,979,9118,19089,8343,3959,10137,16159, %U A339639 3937,10611,15207,20433,32184,17516,19782,37001,15197,23009,40096,50499,27504,26055 %N A339639 a(n) is the sum of the Wieferich and Wall-Sun-Sun residues of prime(n). %C A339639 If a(n) = 0 then prime(n) is both a Wieferich prime (A001220) and a Wall-Sun-Sun (Fibonacci-Wieferich) prime. %C A339639 If the first case of Fermat's last theorem fails for a prime p, that prime is both a Wieferich prime (cf. Wieferich, 1909) and a Wall-Sun-Sun prime (cf. Sun, 1992). %H A339639 Zhi-Wei Sun, <a href="https://doi.org/10.4064/aa-60-4-371-388">Fibonacci numbers and Fermat's last theorem</a>, Acta Arithemtica, Vol. 60, No. 4 (1992), 371-388. %H A339639 A. Wieferich, <a href="http://resolver.sub.uni-goettingen.de/purl?GDZPPN002166968">Zum letzten Fermat'schen Theorem</a>, Journal für die reine und angewandte Mathematik, 136 (1909), 293-302, DOI:<a href="https://doi.org/10.1515/crll.1909.136.293">10.1515/crll.1909.136.293</a>. %F A339639 a(n) = A196202(n) + A113650(n) - 1. %o A339639 (PARI) a(n) = my(p=prime(n)); lift(Mod([1, 1; 1, 0]^(p-kronecker(p, 5)), p^2)[1, 2]) + lift(Mod(2, p^2)^(p-1)) - 1 %Y A339639 Cf. A001220, A113650, A196202. %K A339639 nonn %O A339639 1,1 %A A339639 _Felix Fröhlich_, Dec 11 2020