OFFSET
1,1
COMMENTS
a(17) > 2*10^9. - Hiroaki Yamanouchi, Sep 19 2014
EXAMPLE
phi(phi(126)) = phi(36) = 12 and the sum of the prime factors of 126 = 2 * 3^2 * 7 is 2 + 3 + 7 = 12. Hence 126 belongs to the sequence.
MATHEMATICA
Select[Range[2, 10^5], EulerPhi[EulerPhi[ # ]] == Apply[Plus, Transpose[FactorInteger[ # ]][[1]]] &]
PROG
(Python)
from sympy import primefactors, totient as phi
def ok(n): return n and phi(phi(n)) == sum(primefactors(n))
print([k for k in range(10**6) if ok(k)]) # Michael S. Branicky, Jun 19 2023
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Joseph L. Pe, Oct 15 2002
EXTENSIONS
a(15)-a(16) from Hiroaki Yamanouchi, Sep 19 2014
STATUS
approved