EN
Denote by 𝔠 any set of cardinality continuum. It is proved that a Banach algebra A with the property that for every collection ${a_{α}: α ∈ 𝔠} ⊂ A$ there exist α ≠ β ∈ 𝔠 such that $a_{α} ∈ a_{β}A^{#}$ is isomorphic to
$⨁_{i=1}^{r} (ℂ[X]/X^{d_{i}}ℂ[X]) ⊕ E$,
where $d₁,...,d_{r} ∈ ℕ$, and E is either $Xℂ[X]/X^{d₀}ℂ[X]$ for some d₀ ∈ ℕ or a 1-dimensional $⨁_{i=1}^{r} ℂ[X]/X^{d_{i}}ℂ[X]$-bimodule with trivial right module action. In particular, ℂ is the unique non-zero prime Banach algebra satisfying the above condition.