A172042 a(n) = A000010(A083553(n)).

1, 4, 8, 16, 32, 64, 96, 120, 240, 192, 288, 384, 384, 528, 1056, 1344, 896, 960, 960, 1152, 1728, 1920, 3200, 2560, 2560, 2560, 3328, 3744, 3456, 4032, 3456, 6144, 5632, 6336, 5760, 5760, 7776, 8856, 13776, 14784, 8448, 8640, 9216, 10752, 10080, 8640

Offset: 1

Author

Giovanni Teofilatto, Jan 24 2010

Keywords

• easy
• nonn

Comments

Except for the first term, a(n) is divisible by 4.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A083553.

Programs

Maple

A083553 := proc(n) (ithprime(n+1)-1)*(ithprime(n)-1) ; end proc: A172042 := proc(n) numtheory[phi](A083553(n)) ; end proc: seq(A172042(n),n=1..80) ; # R. J. Mathar, Jan 30 2010

Mathematica

Table[EulerPhi[(Prime[n + 1] - 1)*(Prime[n] - 1)], {n, 1, 50}] (* Amiram Eldar, Apr 09 2021 *)

PARI

a(n)=my(p=prime(n));eulerphi((p-1)*(nextprime(p+1)-1)) \\ Charles R Greathouse IV, Mar 05 2013

Extensions

a(2) inserted and terms beyond a(10) added by R. J. Mathar, Jan 30 2010