A056742 a(n) = phi(2^n - 1)/2.

1, 3, 4, 15, 18, 63, 64, 216, 300, 968, 864, 4095, 5292, 13500, 16384, 65535, 69984, 262143, 240000, 889056, 1320352, 4105040, 3317760, 16200000, 22358700, 56733696, 66382848, 266913216, 267300000, 1073741823, 1073741824

Offset: 2

Author

Robert G. Wilson v, Aug 14 2000

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 2..1206

Crossrefs

Cf. A000010, A000225, A011260, A053287.

Programs

Mathematica

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

PARI

a(n) = eulerphi(2^n - 1)/2; \\ Amiram Eldar, Jun 09 2024

Formula

a(n) = A000010(A000225(n))/2 = A053287(n)/2. - Amiram Eldar, Jun 09 2024