C :

#include<stdio.h>

	double myfunction(int n,double x)
	{
		if(0==n)
		return 1;
		else if(1==n)
		return x;
		else return((2*n-1)*x*myfunction(n-1,x)-(n-1)*myfunction(n-2,x))/n;
	}
int main()
	{
		int n;
		double x;
		double result;
		scanf("%d %lf",&n,&x);
		result=myfunction(n,x);
		printf("%.4f\n",result);
		return 0; 
		
	}

C++ :

#include <stdio.h>
#include <math.h>
int main() {
	float legendre(int n, float x);
	int n;
	float x;
	scanf("%d%f", &n, &x);
	printf("%.4f\n", legendre(n, x));
	return 0;
}
float legendre(int n, float x) {
	if (n == 0)
		return 1;
	if (n == 1)
		return x;
	return ((2 * n - 1) * x * legendre(n - 1, x) - (n - 1) * legendre(n - 2, x)) / n;
}

Pascal :

var
  n:longint;
  x:double;

function legendre(n:longint; x:double):double;
begin
  if(n=0) then exit(1);
  if(n=1) then exit(x);
  legendre:=( (2*n-1)*x*legendre(n-1,x)-
    (n-1)*legendre(n-2,x) ) / n;
end;

begin
  readln(n,x);
  writeln( legendre(n,x):0:4 );
end.