A053285 Totient of 2^n+1.

1, 2, 4, 6, 16, 20, 48, 84, 256, 324, 800, 1364, 3840, 5460, 12544, 19800, 65536, 87380, 186624, 349524, 986880, 1365336, 3345408, 5592404, 16515072, 20250000, 52306176, 84768120, 252645120, 351847488, 760320000, 1431655764, 4288266240, 5632621632, 13628740608

Offset: 0

Author

Labos Elemer, Mar 03 2000

Keywords

• nonn
• changed

Examples

			It is a power of 2 iff n is a Fermat prime.
		

Links

• Max Alekseyev, Table of n, a(n) for n = 0..1128 (terms 0..300 from Robert Israel; terms 301..1062 from Amiram Eldar)

Crossrefs

Cf. A000010, A000225, A002587, A000051, A046798, A046799, A049479, A051953, A054992.

Programs

Magma

[EulerPhi(2^n+1) : n in [1..40]]; // Vincenzo Librandi, Aug 12 2015

Maple

seq(numtheory:-phi(2^n+1), n=0..50); # Robert Israel, Aug 12 2015

Mathematica

Table[EulerPhi[2^n + 1], {n, 35}] (* Vincenzo Librandi, Aug 12 2015 *)

PARI

vector(40, n, eulerphi(2^n+1)) \\ Michel Marcus, Aug 12 2015

Formula

a(n) = A000010(A000051(n)).

Extensions

a(0)=1 prepended by Alois P. Heinz, Aug 12 2015