package main
import (
"fmt"
"math/big"
)
/*
This program computes the factorial of numbers greater than 20.
Go's math/big package provides big.Int, an arbitrary‑precision
integer type that can represent extremely large numbers safely.
*/
/*
Compute factorial using big.Int.
The algorithm multiplies numbers from 2 to n.
big.Int handles overflow internally and grows as needed.
*/
func factorialBig(n int64) *big.Int {
result := big.NewInt(1)
for i := int64(2); i <= n; i++ {
result.Mul(result, big.NewInt(i))
}
return result
}
/*
Main entry point: read input, compute factorial, print result.
*/
func main() {
var n int64
fmt.Print("Enter a number greater than 20: ")
fmt.Scan(&n)
result := factorialBig(n)
fmt.Printf("\nFactorial of %d is:\n\n", n)
fmt.Println(result.String())
}
/*
run:
Enter a number greater than 20: 25
Factorial of 25 is:
15511210043330985984000000
*/
