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 A366602 #27 Mar 15 2025 14:11:31
%S A366602 2,4,6,8,8,24,8,16,32,48,16,96,8,64,96,32,8,512,8,192,144,128,16,768,
%T A366602 128,128,160,256,64,4608,8,128,384,128,512,8192,32,128,192,768,32,
%U A366602 9216,32,1024,4096,512,64,6144,32,8192,1536,1024,64,10240,3072,2048,384
%N A366602 Number of divisors of 4^n-1.
%H A366602 Max Alekseyev, <a href="/A366602/b366602.txt">Table of n, a(n) for n = 1..1128</a>
%F A366602 a(n) = sigma0(4^n-1) = A000005(A024036(n)).
%F A366602 a(n) = A046801(2*n) = A046798(n) * A046801(n). - _Max Alekseyev_, Jan 07 2024
%e A366602 a(4)=8 because 4^4-1 has divisors {1, 3, 5, 15, 17, 51, 85, 255}.
%p A366602 a:=n->numtheory[tau](4^n-1):
%p A366602 seq(a(n), n=1..100);
%t A366602 DivisorSigma[0,4^Range[100]-1] (* _Paolo Xausa_, Oct 14 2023 *)
%o A366602 (PARI) a(n) = numdiv(4^n-1);
%Y A366602 Cf. A024036, A000005, A057957, A295501, A366603, A366604.
%Y A366602 Cf. A046798, A046801, A366575, A366612, A366621, A366633, A366652, A366661, A070528, A366683, A366709.
%K A366602 nonn
%O A366602 1,1
%A A366602 _Sean A. Irvine_, Oct 14 2023