OFFSET
1,2
COMMENTS
Except for the first term, a(n) is divisible by 4.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
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 *)
PROG
(PARI) a(n)=my(p=prime(n)); eulerphi((p-1)*(nextprime(p+1)-1)) \\ Charles R Greathouse IV, Mar 05 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Giovanni Teofilatto, Jan 24 2010
EXTENSIONS
a(2) inserted and terms beyond a(10) added by R. J. Mathar, Jan 30 2010
STATUS
approved