text: power23 [ ] will store pairwise product of elements of power2 and power3 that are <= r
code: Vector < Integer > power23 = new Vector < Integer > ( ) ; for ( int x = 0 ; x < power2 . size ( ) ; x ++ ) { for ( int y = 0 ; y < power3 . size ( ) ; y ++ ) { int mul = power2 . get ( x ) * power3 . get ( y ) ; if ( mul == 1 ) continue ;