Why is the f-16 aircraft called the f-16?

The US Air Force identifies their operational aircraft by model numbers that follow a letter code. The codes are: F - fighter aircraft, A-ground attack, B- bomber aircraft, C- cargo aircraft, X- experimental. Many years ago, the military used other code identifiers that are may not by used: P- pursuit aircraft, O- observation, H- helicopter.

The F-16 is the 16th fighter design built during the jet age. It was built after the F-15.

What confuses me is how did they jump up to F-117 for the Stealth Fighter?