R 5 4 7 2 July 8, 2019 16 32 64 128 5 r 7 )= 3 r 4 )- 27 R 4 - 5 or 2r 7 3 R 4 - 5 or 2r 7 ≤ 3 R 5 4 r 2 3 7 7 2r 4 r 5 R 5 7 54+ 7 5 4 - 7 2
