This was conjectured in 1913 by Indian mathematician Srinivasa Ramanujan, proposed independently in 1943 by the Norwegian mathematician Wilhelm Ljunggren, and proved in 1948 by the Norwegian mathematician Trygve Nagell.
Detta förmodades 1913 av den indiska matematikern Srinivasa Ramanujan och oberoende av honom 1943 av den norska matematikern Wilhelm Ljunggren, och bevisades av den norska matematikern Trygve Nagell 1948.