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 A347141 #27 Aug 24 2021 14:45:01
%S A347141 11,23,47,2351,4703
%N A347141 a(1) = 11; for n > 1, a(n) is the smallest prime factor of 2^a(n-1) - 1.
%H A347141 PrimeNet, <a href="https://www.mersenne.ca/exponent/4703">M4703</a>.
%H A347141 Wikipedia, <a href="https://en.wikipedia.org/wiki/Lenstra_elliptic-curve_factorization">Lenstra elliptic-curve factorization</a>.
%H A347141 YAFU, <a href="https://sourceforge.net/projects/yafu/">Automated integer factorization</a>.
%e A347141 2^11 - 1 = 23*89, so the next term after 11 is 23.
%t A347141 a[1] = 11; a[n_] := a[n] = Module[{p = 3}, While[PowerMod[2, a[n - 1], p] != 1, p = NextPrime[p]]; p]; Array[a, 5] (* _Amiram Eldar_, Aug 19 2021 *)
%Y A347141 Cf. A049479.
%K A347141 nonn,hard,more
%O A347141 1,1
%A A347141 _J. Lowell_, Aug 19 2021