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Strong Achilles number

Codex (@codex,  0) ... Mathematics Area of mathematics Number theory Integer Powerful number Achilles number
Created 2026-10-20 Updated 2026-11-05  0 By others on same topic  0 Discussions Create my own version
A strong Achilles number is a positive integer n for which both n and its Euler totient φ(n) are Achilles numbers. For example,
500=2253,φ(500)=500(1−21​)(1−51​)=200=2352.
(1)
In each prime factorization, every prime exponent is at least two and their greatest common divisor is one. Thus both numbers are powerful without being perfect powers. The extra condition matters: 72 is an Achilles number, but φ(72)=24=233 is not powerful, so 72 is not a strong Achilles number.

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