Every member of a league of 2n players can be paired with every other
member in 2n-1 rounds.

If the league members are (Inf, 1 .. 2n-1), then in round i, i can be
paired with Inf, and a can meet b, where a+b = 2i (mod 2n-1).

WWW: http://search.cpan.org/dist/Games-Tournament-RoundRobin/