double res(int k,int a) {
    double zn1 = 0.5772;
    double zn2 = 0.5772;
    for (int i = 0; i < k; i++)
        zn1 += 1.0/i;
    for (int i = 0; i < k; i++)
        zn2 += 1.0/(a + i);
    return (zn1 + zn2);
    }
double vtor(int a,double x)
{
    double sum = 0;
    double zn = 0;
    double sum1 = 0;
    for (int i = 0; i < a; i++)
    {
        zn = (fact(a - i - 1)*pow(pow(x,2)/4,i))/fact(i);
        sum += zn;
    }
    for(int i = 0; i < 10; i++)
        sum1 += res(i,a)*pow(-pow(x,2)/4,i)/(fact(i)*fact(a + i));
    return (((-pow(x/2,-a)*sum)/(3.141592)) + (2*perv(a,x)*log(x/2)/(3.141592)) - (pow((x/2),a)*sum1/(3.141592)));
}