Find the count of numbers that can be formed using digits 3 , 4 only and having length at max N . | Function to find the count of numbers that can be formed using digits 3 , 4 only and having length at max N . ; Driver code
< ? php function numbers ( $ n ) { return ( pow ( 2 , $ n + 1 ) ) - 2 ; } $ n = 2 ; echo numbers ( $ n ) ; ? >