Sum of all i such that ( 2 ^ i + 1 ) % 3 = 0 where i is in range [ 1 , n ] | Function to return the required sum ; Total odd numbers from 1 to n ; Sum of first n odd numbers ; Driver code
< ? php function sumN ( $ n ) { $ n = ( int ) ( ( $ n + 1 ) / 2 ) ; return ( $ n * $ n ) ; } $ n = 3 ; echo sumN ( $ n ) ; ? >