1 / 2 x ( 1 + 1 / 1x3 ) x (1+ 1 / 2x4 ) x (1+ 1 / 3x5 )

1 / 2 x ( 1+ 1 / 1x3 ) x (1+ 1 / 2x4 ) x (1+ 1 / 3x5 ) x...x (1+ 1 / 2019x2021