text: Sum of divisors of factorial of a number | C # program to find sum of divisors in n ! ; allPrimes [ ] stores all prime numbers less than or equal to n . ; Fills above vector allPrimes [ ] for a given n ; Create a boolean array " prime [ 0 . . n ] " and initialize all entries it as true . A value in prime [ i ] will finally be false if i is not a prime , else true . ; Loop to update prime [ ] ; If prime [ p ] is not changed , then it is a prime ; Update all multiples of p ; Store primes in the vector allPrimes ; Function to find all result of factorial number ; Initialize result ; find exponents of all primes which divides n and less than n ; Current divisor ; Find the highest power ( stored in exp ) ' ▁ ▁ of ▁ allPrimes [ i ] ▁ that ▁ divides ▁ n ▁ using ▁ ▁ Legendre ' s formula . ; Using the divisor function to calculate the sum ; return total divisors ; Driver program to run the cases
code: using System ; using System . Collections ; class GFG { static ArrayList allPrimes = new ArrayList ( ) ; static void sieve ( int n ) { bool [ ] prime = new bool [ n + 1 ] ; for ( int p = 2 ; p * p <= n ; p ++ ) { if ( prime [ p ] == false ) { for ( int i = p * 2 ; i <= n ; i += p ) prime [ i ] = true ; } } for ( int p = 2 ; p <= n ; p ++ ) if ( prime [ p ] == false ) allPrimes . Add ( p ) ; } static int factorialDivisors ( int n ) { int result = 1 ; for ( int i = 0 ; i < allPrimes . Count ; i ++ ) { int p = ( int ) allPrimes [ i ] ; int exp = 0 ; while ( p <= n ) { exp = exp + ( n / p ) ; p = p * ( int ) allPrimes [ i ] ; } result = result * ( ( int ) Math . Pow ( ( int ) allPrimes [ i ] , exp + 1 ) - 1 ) / ( ( int ) allPrimes [ i ] - 1 ) ; } return result ; } static void Main ( ) { Console . WriteLine ( factorialDivisors ( 4 ) ) ; } }