C :

#include<stdio.h>
long long int f(n)
{

   long long int a;
    if(n==1)
    a=0;
    if(n==2)
    a=1;
    if(n>2)
    a=(n-1)*(f(n-2)+f(n-1));
    return a;
}
void main()
{
    int c;
    ;
    while(scanf("%d",&c)==1)
    {

         printf("%.lld\n",f(c));

    }
}

C++ :

#include<stdio.h>

int main()
{
	long long a[21]={0,0,1};
	int n,i;
	for(i=3;i<=20;i++)
		a[i]=(i-1)*a[i-1]+(i-1)*a[i-2];
	while(scanf("%d",&n)!=EOF)
		printf("%lld\n",a[n]);
	return 0;
}

Pascal :

program letter;
var n,i:longint;
    a:array[1..20] of int64;
begin
  a[1]:=0;
  a[2]:=1;
  for i:=3 to 20 do
    a[i]:=(i-1)*(a[i-1]+a[i-2]);
  while not(eof) do
    begin
       readln(n);
       writeln(a[n]);
    end;
end.

Java :

import java.math.BigInteger;
import java.util.Scanner;

public class Main {

	private static int N = 25;
	private static BigInteger[] factorial = new BigInteger[25];
	private static BigInteger[] result = new BigInteger[25];
	private static BigInteger notInit = BigInteger.valueOf(-1);

	static {
		factorial[0] = BigInteger.valueOf(1);
		for (int i = 1; i < N; i++) {
			factorial[i] = factorial[i - 1].multiply(BigInteger.valueOf(i));
			result[i] = notInit;
		}

		result[0] = BigInteger.valueOf(0);
		result[1] = BigInteger.valueOf(0);
		result[2] = BigInteger.valueOf(1);
	}

	public static BigInteger combination(int m, int n) {
		return (factorial[n].divide(factorial[n - m])).divide(factorial[m]);
	}

	public static BigInteger noteasy(int n) {

		BigInteger finalResult = null;

		if (!result[n].equals(notInit)) {
			finalResult = result[n];
		} else {
			finalResult = factorial[n];
			for (int i = 1; i <= n - 2; i++) {

				finalResult = finalResult.subtract(combination(i, n).multiply(
						noteasy(n - i)));
			}
			finalResult = finalResult.subtract(BigInteger.valueOf(1));
			result[n] = finalResult;
		}

		return finalResult;

	}

	public static void main(String[] args) {

		Scanner cin = new Scanner(System.in);
		while (cin.hasNext()) {
			int n = cin.nextInt();
			System.out.println(noteasy(n));

		}

	}

}