Fatto generale: 1681 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1681 is a square and each of its two 2-digit parts is square.
Trivia: 1681 is an unremarkable number.
Data storica: August 7th is the day in 1955 that Tokyo Telecommunications Engineering, the precursor to Sony, sells its first transistor radios in Japan.