Beal's theorem
Equation [math]\displaystyle{ a^m + b^n = c^k }[/math] where [math]\displaystyle{ a, b, c, d, e, r, s \in \mathbb{N}^{*} }[/math] and [math]\displaystyle{ k, m, n \in \mathbb{N}_{\ge 3} }[/math] implies [math]\displaystyle{ d := }[/math] gcd[math]\displaystyle{ (a, b, c) \gt 1. }[/math]
Indirect proof: Put necessarily [math]\displaystyle{ (da)^n + (db)^m = (dc)^n }[/math] to cancel [math]\displaystyle{ d }[/math] after computing mod [math]\displaystyle{ d }[/math]. Multiply [math]\displaystyle{ b^s + e^m = c^s }[/math] generalised by [math]\displaystyle{ d^{rm} }[/math] again to yield [math]\displaystyle{ b = 1 }[/math], [math]\displaystyle{ c = d }[/math] and [math]\displaystyle{ s \ne m \notin 2\mathbb{N} }[/math]. The second general form [math]\displaystyle{ 1 + d^s = e^m }[/math] shows likewise the claim by contradiction for [math]\displaystyle{ m \ne s \notin 2\mathbb{N} }[/math].[math]\displaystyle{ \square }[/math]
Conclusion: Due to [math]\displaystyle{ m \ne s }[/math], no [math]\displaystyle{ n \in {}^{\omega}\mathbb{N}_{\ge 3} }[/math] satisfies [math]\displaystyle{ a^n + b^n = c^n }[/math] for arbitrary [math]\displaystyle{ a, b, c \in {}^{\omega}\mathbb{N}^{*} }[/math].