Odd numbers in N | Function to get no of set bits in binary representation of positive integer n ; Count number of 1 's in binary  representation of n. ; Number of odd numbers in n - th row is 2 raised to power the count . ; Driver code
< ? php function countSetBits ( $ n ) { $ count = 0 ; while ( $ n ) { $ count += $ n & 1 ; $ n >>= 1 ; } return $ count ; } function countOfOddsPascal ( $ n ) { $ c = countSetBits ( $ n ) ; return pow ( 2 , $ c ) ; } $ n = 20 ; echo countOfOddsPascal ( $ n ) ; ? >