Naive Go factorial. Can't run in Go playground, too slow.

factorial.go

// real	0m0.638s
// user	0m0.621s
// sys	0m0.015s
package main

import (
	"fmt"
	"math/big"
)

func f(n int64) *big.Int {
	ret := big.Int{}
	return ret.MulRange(1, n)
}

func main() {
	fmt.Println(f(100000))
}