A366607 - OEIS

%I #23 Mar 15 2025 14:13:48

%S 3,6,18,84,258,1302,4356,20520,65538,351120,1110276,5048232,17041416,

%T 82623888,284225796,1494039792,4301668356,20788904016,73234343952,

%U 332019460560,1103789883396,5936210280000,18679788287496,84884999116320,282937726148616

%N Sum of the divisors of 4^n+1.

%H Max Alekseyev, <a href="/A366607/b366607.txt">Table of n, a(n) for n = 0..583</a>

%F a(n) = sigma(4^n+1) = A000203(A052539(n)).

%F a(n) = A069061(2*n). - _Max Alekseyev_, Jan 08 2024

%e a(3)=84 because 4^3+1 has divisors {1, 5, 13, 65}.

%p a:=n->numtheory[sigma](4^n+1):

%p seq(a(n), n=0..100);

%t DivisorSigma[1,4^Range[0,30]+1] (* _Paolo Xausa_, Oct 14 2023 *)

%o (Python)

%o from sympy import divisor_sigma

%o def A366607(n): return divisor_sigma((1<<(n<<1))+1) # _Chai Wah Wu_, Oct 14 2023

%Y Cf. A000203, A052539, A057940, A274903, A366603, A366605, A366606, A366608, A366609.

%Y Cf. A069061, A366578, A366617, A366629, A366638, A366657, A366666, A366668, A366689, A366715.

%K nonn

%O 0,1

%A _Sean A. Irvine_, Oct 14 2023