Linked from
The 18 pages that link to Peano arithmetic, each with the reason it gives.
Kurt GödelBroader topic: Gödel encoded statements about proofs within arithmetic of this kind.
DecidabilityCompared with: Unlike Presburger arithmetic, the set of its theorems is not decidable.
Peano axiomsBroader topic: It develops the first-order Peano axioms into an arithmetic theory.
Goodstein's theoremRelated: Goodstein's theorem is true but has no proof in this theory.
Gödel sentenceRelated: It is a standard setting rich enough to encode its own formulas and proofs.