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%I #21 Jan 07 2024 14:19:05
%S 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 128,128,160,256,64,4608,8,128,384,128,512,8192,32,128,192,768,32,
%U 9216,32,1024,4096,512,64,6144,32,8192,1536,1024,64,10240,3072,2048,384
%N Number of divisors of 4^n-1.
%H Max Alekseyev, <a href="/A366602/b366602.txt">Table of n, a(n) for n = 1..1122</a>
%F a(n) = sigma0(4^n-1) = A000005(A024036(n)).
%F a(n) = A046801(2*n) = A046798(n) * A046801(n). - _Max Alekseyev_, Jan 07 2024
%e a(4)=8 because 4^4-1 has divisors {1, 3, 5, 15, 17, 51, 85, 255}.
%p a:=n->numtheory[tau](4^n-1):
%p seq(a(n), n=1..100);
%t DivisorSigma[0,4^Range[100]-1] (* _Paolo Xausa_, Oct 14 2023 *)
%o (PARI) a(n) = numdiv(4^n-1);
%Y Cf. A024036, A000005, A057957, A295501, A366603, A366604.
%Y Cf. A046798, A046801, A366575, A366612, A366621, A366633, A366652, A366661, A070528, A366683, A366709.
%K nonn
%O 1,1
%A _Sean A. Irvine_, Oct 14 2023
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