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 A321213 #24 Sep 08 2022 08:46:23
%S A321213 2,2,2,2,2,4,4,4,4,8,16,32
%N A321213 a(n) is the number of divisors of n-th Fermat number (A000215).
%F A321213 a(n) = A000005(A000215(n)). - _Omar E. Pol_, Oct 31 2018
%F A321213 a(n) = 2^A046052(n) for squarefree A000215(n). - _Amiram Eldar_, Oct 31 2018
%e A321213 A000215(n) is prime for n=0 to 4, so a(n)= 2 for n=0 to 4.
%t A321213 Table[DivisorSigma[0, 2^2^n + 1], {n, 120}]
%o A321213 (PARI) a(n) = numdiv(2^2^n+1)
%o A321213 (Magma) [DivisorSigma(0, 2^2^n + 1): n in [1..100]]
%o A321213 (GAP) List(List([0..11],n->2^(2^n)+1),i->Number(DivisorsInt(i))); # _Muniru A Asiru_, Nov 03 2018
%Y A321213 Cf. A000005, A000215.
%K A321213 nonn,more,hard
%O A321213 0,1
%A A321213 _Jinyuan Wang_, Oct 31 2018
%E A321213 a(10)-a(11) from _Amiram Eldar_, Oct 31 2018