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