Finite geometry: The Bruck-Ryser-Chowla Theorem. If a finite projective plane of order q exists and q is congruent to 1 or 2 (mod 4), then q must be the sum of two squares.
BRC also has the distinction of being the la(te)st non-trivial theorem in finte geometry/design theory, as it's been the best result on existence of planes/designs of a given order for the past 60 years.

Finite geometry: The Bruck-Ryser-Chowla Theorem. If a finite projective plane of order q exists and q is congruent to 1 or 2 (mod 4), then q must be the sum of two squares.
BRC also has the distinction of being the la(te)st non-trivial theorem in finte geometry/design theory, as it's been the strongest result on existence of projective planes/symmetric designs for a given class of orders q for the past 60 years. 

Finite geometry: The Bruck-Ryser-Chowla Theorem

Finite geometry: The Bruck-Ryser-Chowla Theorem. If a finite projective plane of order q exists and q is congruent to 1 or 2 (mod 4), then q must be the sum of two squares.
BRC also has the distinction of being the la(te)st non-trivial theorem in finte geometry/design theory, as it's been the best result on existence of planes/designs of a given order for the past 60 years.