Trump will be the seventh US President to have not held any elected office before winning a national election. The previous six were Zachary Taylor, Ulysses S Grant, Chester A Arthur, William Howard Taft, Herbert Hoover and Dwight Eisenhower. Of those six, Taylor, Grant and Eisenhower were all generals, Arthur was a Vice-President who became President and Taft and Coolidge were both Cabinet secretaries before being elected. Arthur is the only one without any real federal-level political experience upon becoming President, having been involved in New York Republican politics before being brought in to balance the ticket with Garfield and then becoming President after just six months as Vice-President.
In short, Trump is a massive outlier in terms of pre-Presidential experience.
The other bit of trivia (and coincidence) is about his wife. Melania Trump will be the first First Lady to be born outside the US since Louisa Adams (wife of John Quincy Adams). Her husband is the only President to date to have followed three consecutive two-term Presidents (Jefferson, Madison and Monroe). Assuming Obama makes it to the end of his second term in January, Trump will be the second (following Clinton, GW Bush and Obama). To add to the coincidence, both those periods were preceded by a two-term President being succeeded by his Vice-President for a single term (Washington and Adams, Reagan and GHW Bush). This coincidence led me to predict a Jeb Bush presidency four years ago having decided that ‘son of the one term President’ was the important factor in history repeating, rather than ‘having a wife born outside the US’.
Those of you looking for a silver lining will take heart in the fact that, like his father, John Quincy Adams only served a single term in office. Those of you expecting it all to get worse will likely note that he was succeeded by Andrew Jackson.