OFFSET
1,1
COMMENTS
phi(p*q) = (p-1)(q-1) where p, q are distinct safe primes.
2^(a(n)/2) == 1 (mod A157352(n)). For the reference see a comment on A269454. - Wolfdieter Lang, Mar 31 2016
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1500
FORMULA
a(n) = phi(A157352(n)), n >= 1.
MATHEMATICA
EulerPhi /@ Select[Select[Range@ 4000, PrimeNu@ # == 2 &], Times @@ Map[If[PrimeQ[(# - 1)/2], #, 0] &, Map[First, FactorInteger@ #]] == # &] (* Michael De Vlieger, Feb 28 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Marina Ibrishimova, Feb 27 2016
EXTENSIONS
More terms from Michael De Vlieger, Feb 28 2016
STATUS
approved