A027742 a(n) = phi(4^n-1)/(2*n).

1, 2, 6, 16, 60, 144, 756, 2048, 7776, 24000, 120032, 276480, 1719900, 4741632, 17820000, 67108864, 336849900, 725594112, 4822382628, 11842560000, 57802864896, 200778006528, 998132265920, 2283043553280, 13122000000000, 44980696051200, 178118842613760

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1122

Crossrefs

Cf. A000010, A027695, A295501.

Programs

Mathematica

Table[EulerPhi[4^n-1]/(2n),{n,30}] (* Harvey P. Dale, May 01 2013 *)

PARI

a(n) = eulerphi(4^n-1)/(2*n) \\ Felix Fröhlich, Dec 02 2019

Formula

a(n) = A295501(n)/(2*n) = A027695(n)/2. - Amiram Eldar, Nov 30 2024

Extensions

Offset corrected by Sean A. Irvine, Dec 02 2019