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A053285
Totient of 2^n+1.
13
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
OFFSET
0,2
LINKS
Max Alekseyev, Table of n, a(n) for n = 0..1122 (terms 0..300 from Robert Israel; terms 301..1062 from Amiram Eldar)
FORMULA
a(n) = A000010(A000051(n)).
EXAMPLE
It is a power of 2 iff n is a Fermat prime.
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 *)
PROG
(PARI) vector(40, n, eulerphi(2^n+1)) \\ Michel Marcus, Aug 12 2015
(Magma) [EulerPhi(2^n+1) : n in [1..40]]; // Vincenzo Librandi, Aug 12 2015
KEYWORD
nonn
AUTHOR
Labos Elemer, Mar 03 2000
EXTENSIONS
a(0)=1 prepended by Alois P. Heinz, Aug 12 2015
STATUS
approved