VOOZH about

URL: https://oeis.org/A075863

⇱ A075863 - OEIS

login
A075863
Numbers k such that phi(phi(k)) = sum of prime factors of k.
0
8, 45, 55, 95, 126, 132, 198, 215, 228, 516, 2855, 6852, 7655, 18372, 276455, 663492
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
Sequence in context: A181268 A374281 A361490 * A118838 A153828 A247834
KEYWORD
nonn,more
AUTHOR
Joseph L. Pe, Oct 15 2002
EXTENSIONS
a(15)-a(16) from Hiroaki Yamanouchi, Sep 19 2014
STATUS
approved