#include <iostream>
#include <math.h>

using namespace std;

double sum(int n, double a);
double sum_sin();
void formula(int n);

double sum_sin()
{
    double sum = 0;
    for (double i = 0.1; i <= 10; i = i + 0.1)
    {
        sum = sum + (1 + sin(i));
    }
    return sum;
}

double sum(int n, double a)
{
    double sum = 0;
    int fact = 1;
    for (int i = 1; i <= n; i++)
    {
        fact = fact*i;
        sum = sum + a / fact;
    }
    return sum;
}

void formula(int n)
{
    cout << endl;
    float *v = new float[n];
    v[0] = 0; v[1] = 0; v[2] = 1.5;
    for (int i = 3; i<n; i++){
        if (n >= 4)
        {
            cout << v[0] << ' ' << v[1] << ' ' << v[2] << endl;
            v[i] = ((i + 1) / (i*i + 1)*v[i - 1] - v[i - 2] * v[i - 3]);
            cout << i << endl;
        }
        if (n - 1 == i)  cout << "V" << n << "=" << v[i];
    }  cout << endl;
    for (int j = 0; j<n; j++)
        cout << v[j] << ' ';
}

int main()
{
    setlocale(LC_ALL, "Russian");
    int n;
    double a;
    cout << "1 задание. Посчитать a/1! ... a/n!" << endl;
    cout << "n: ";
    cin >> n;
    cout << "a: ";
    cin >> a;
    cout << "Результат: " << sum(n, a) << endl;

    cout << "2 задание. Посчитать 1+sin(0.1) ... 1+sin(10)" << endl;
    cout << "Результат 2: " << sum_sin() << endl;

    cout << "3 задание. Посчитать по формуле" << endl;
    cout << "Введите n:";
    cin >> n;
    if (n >= 4) formula(n);
    else cout << "\aВнимание N < 4!";
}