Not decidable as a result of being neither formally provable nor unprovable.
Undecidable
See also
Gödel's First Incompleteness Theorem, Gödel's Second Incompleteness Theorem, Recursively Undecidable, Rice's Theorem, Richardson's TheoremExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Undecidable." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Undecidable.html