Cassini and Catalan identities
Cassini's identity (sometimes called Simson's identity), Catalan's identity and Vajda's identity are mathematical identities for the Fibonacci numbers. Cassini's identity, a special case of the other two, states that for the nth Fibonacci number, F n − 1 F n + 1 − F n 2 = ( − 1 ) n .
Source: Wikipedia — Cassini and Catalan identities (CC BY-SA 4.0)