OFFSET
1,4
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
For primorials with 10, 100, or 1000 prime factors, their totients have only 5, 32 or 241 prime divisors, corresponding to a(10), a(100), and a(1000).
MATHEMATICA
Table[PrimeNu@ EulerPhi[Product[Prime@ i, {i, n}]], {n, 78}] (* or *)
With[{nn = 78}, PrimeNu@ FoldList[LCM @@ {#1, #2} &, Prime@ Range@ nn - 1]] (* Michael De Vlieger, Jul 14 2017 *)
PROG
(Haskell)
a055768 = a001221 . a005867 -- Reinhard Zumkeller, May 01 2013
(PARI) a(n)=omega(lcm(apply(p->p-1, primes(n)))) \\ Charles R Greathouse IV, Sep 02 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 12 2000
STATUS
approved