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 A366607 #23 Mar 15 2025 14:13:48
%S A366607 3,6,18,84,258,1302,4356,20520,65538,351120,1110276,5048232,17041416,
%T A366607 82623888,284225796,1494039792,4301668356,20788904016,73234343952,
%U A366607 332019460560,1103789883396,5936210280000,18679788287496,84884999116320,282937726148616
%N A366607 Sum of the divisors of 4^n+1.
%H A366607 Max Alekseyev, <a href="/A366607/b366607.txt">Table of n, a(n) for n = 0..583</a>
%F A366607 a(n) = sigma(4^n+1) = A000203(A052539(n)).
%F A366607 a(n) = A069061(2*n). - _Max Alekseyev_, Jan 08 2024
%e A366607 a(3)=84 because 4^3+1 has divisors {1, 5, 13, 65}.
%p A366607 a:=n->numtheory[sigma](4^n+1):
%p A366607 seq(a(n), n=0..100);
%t A366607 DivisorSigma[1,4^Range[0,30]+1] (* _Paolo Xausa_, Oct 14 2023 *)
%o A366607 (Python)
%o A366607 from sympy import divisor_sigma
%o A366607 def A366607(n): return divisor_sigma((1<<(n<<1))+1) # _Chai Wah Wu_, Oct 14 2023
%Y A366607 Cf. A000203, A052539, A057940, A274903, A366603, A366605, A366606, A366608, A366609.
%Y A366607 Cf. A069061, A366578, A366617, A366629, A366638, A366657, A366666, A366668, A366689, A366715.
%K A366607 nonn
%O A366607 0,1
%A A366607 _Sean A. Irvine_, Oct 14 2023