%I #8 Jun 09 2024 09:05:19

%S 1,3,4,15,18,63,64,216,300,968,864,4095,5292,13500,16384,65535,69984,

%T 262143,240000,889056,1320352,4105040,3317760,16200000,22358700,

%U 56733696,66382848,266913216,267300000,1073741823,1073741824

%N a(n) = phi(2^n - 1)/2.

%H Amiram Eldar, <a href="/A056742/b056742.txt">Table of n, a(n) for n = 2..1206</a>

%F a(n) = A000010(A000225(n))/2 = A053287(n)/2. - _Amiram Eldar_, Jun 09 2024

%t Table[EulerPhi[(2^n - 1)]/2, {n, 2, 40}]

%o (PARI) a(n) = eulerphi(2^n - 1)/2; \\ _Amiram Eldar_, Jun 09 2024

%Y Cf. A000010, A000225, A011260, A053287.

%K nonn

%O 2,2

%A _Robert G. Wilson v_, Aug 14 2000