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 A180471 #16 Mar 28 2021 07:03:59
%S A180471 31,257,73,89,683,113,11,151,331,73,109,61681,127,337,5419,178481,
%T A180471 2796203,157,1613,233,1103,2089,3033169,1321,20857,599479,281,86171,
%U A180471 122921,19,37,109,433,38737,2731,8191,121369,22366891,13367,164511353,8831418697,23,353,397,683,2113,2931542417
%N A180471 Irregular triangle in which row n has all primes q such that prime(n)*q is a base-2 Fermat pseudoprime.
%C A180471 The length of row n is A085014(n). The smallest and largest primes in row n are A085012(n) and A085019(n).
%D A180471 See A085012.
%H A180471 Amiram Eldar, <a href="/A180471/b180471.txt">Table of n, a(n) for n = 5..3424</a>
%H A180471 <a href="/index/Ps#pseudoprimes">Index entries for sequences related to pseudoprimes</a>
%e A180471 The irregular triangle begins
%e A180471 31
%e A180471 none
%e A180471 257
%e A180471 73
%e A180471 89, 683
%e A180471 113
%e A180471 11, 151, 331
%e A180471 73, 109
%e A180471 61681
%t A180471 Flatten[Table[p=Prime[n]; q=Transpose[FactorInteger[2^(p-1)-1]][[1]]; cnt={}; Do[If[PowerMod[2, p*q[[i]]-1, p*q[[i]]]==1, AppendTo[cnt,q[[i]]]], {i,Length[q]}]; cnt, {n,5,50}]]
%Y A180471 Cf. A085012, A085014, A085019.
%K A180471 nonn,tabf
%O A180471 5,1
%A A180471 _T. D. Noe_, Jan 19 2011