Fatto matematico: 653 is the only known prime for which 5 is neither a primitive root or a quadratic residue of 4n^{2}+1.
Trivia: 653 is an unremarkable number.
Data storica: October 14th is the day in 1939 that the German submarine U-47 sinks the British battleship HMS Royal Oak within her harbour at Scapa Flow, Scotland.