For those who were, like me, scratching their head over the number of teams in the NCAA men’s basketball tournament, this from Wikipedia explains the number, if not the apparently arbitrary reasoning behind it.
Two low-seeded teams (typically teams with poor records that qualified by winning their conference tournament championships) play the “opening round” game to determine which will advance into the first round of the tournament, with the winner advancing to play the top seed in one of the four regions. The opening Round game was added in 2001 and has been played in University of Dayton Arena in Dayton, Ohio each subsequent year. The opening round is considered part of the tournament and is often referred to as a “play-in” game.
There have been 64 teams since 1985, with the 65-team “play-in” format since 2001. The women’s tournament has 64 teams, so no play-in game.