general_fact: 351 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 351 is the smallest number so that it and the surrounding numbers are all products of 4 or more primes.
trivia: 351 is an uninteresting number.
historical_date: December 16th is the day in 1497 that Vasco da Gama rounds the Cape of Good Hope, the point where Bartolomeu Dias had previously turned back to Portugal.