( 100 - 1^2 ) . ( 100 - 2^2 ) ... ( 100 - 2020^2 )
= ( 100 - 1^2 ) . ( 100 - 2^2 ) ... . ( 100 - 10^2 ) . ... . ( 100 - 2020^2 )
= ( 100 - 1^2 ) . ( 100 - 2^2 ) ... . ( 100 - 100 ) . ... . ( 100 - 2020 ^2 )
= ( 100 - 1^2 ) . ( 100 - 2^2 ) ... . 0 . ... . ( 100 - 2020^2 )
= 0