Fatto generale: 28638 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 28638 is an unremarkable number.
Trivia: 28638 is a boring number.
Data storica: May 28th is the day in 1995 that the Russian town of Neftegorsk is hit by a 7.6 magnitude earthquake that kills at least 2,000 people, half of the total population.