Sum of all proper divisors from 1 to N | Utility function to find sum of all proper divisor of number up to N ; Loop to find the proper divisor of every number from 1 to N ; Driver Code
class GFG { static int properDivisorSum ( int n ) { int sum = 0 ; int i ; for ( i = 1 ; i <= n ; ++ i ) sum += ( n / i ) * i ; return sum - n * ( n + 1 ) / 2 ; } public static void main ( String [ ] args ) { int n = 4 ; System . out . println ( properDivisorSum ( n ) ) ; n = 5 ; System . out . println ( properDivisorSum ( n ) ) ; } }