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 A366603 #26 Mar 15 2025 14:12:10
%S A366603 4,24,104,432,1536,8736,22528,111456,473600,1999872,5909760,38054016,
%T A366603 89522176,462274560,2015330304,7304603328,22907191296,166290432000,
%U A366603 366506672128,2220409884672,7645340651520,29833839544320,95821839806976,648494317126656
%N A366603 Sum of the divisors of 4^n-1.
%H A366603 Max Alekseyev, <a href="/A366603/b366603.txt">Table of n, a(n) for n = 1..1128</a> (terms 1..1062 from Robert Israel)
%F A366603 a(n) = sigma(4^n-1) = A000203(A024036(n)).
%F A366603 a(n) = A069061(n) * A075708(n). - _Robert Israel_, Nov 22 2023
%e A366603 a(4)=432 because 4^4-1 has divisors {1, 3, 5, 15, 17, 51, 85, 255}.
%p A366603 a:=n->numtheory[sigma](4^n-1):
%p A366603 seq(a(n), n=1..100);
%t A366603 DivisorSigma[1,4^Range[30]-1] (* _Paolo Xausa_, Oct 14 2023 *)
%Y A366603 Cf. A024036, A000203, A057957, A069061, A075708, A295501, A366602, A366604.
%Y A366603 Cf. A075708, A366576, A366613, A366622, A366634, A366653, A366662, A102146, A366684, A366710.
%K A366603 nonn
%O A366603 1,1
%A A366603 _Sean A. Irvine_, Oct 14 2023