In the National Pokedex what number is Porygon-Z?

Porygon-Z is numbered 474 in the National Pokédex because it is the final evolution of Porygon, a Normal-type Pokémon introduced in Generation I. In the evolutionary line, Porygon evolves into Porygon2 through trade while holding an Up-Grade item, and then Porygon2 can further evolve into Porygon-Z through trade while holding a Dubious Disc. Therefore, as the third and final form of Porygon, Porygon-Z is assigned the number 474 in the National Pokédex.