[HttpGet]
        public async Task<string> Get([FromQuery(Name = "number")] long number)
        {

[HttpGet]
    public string Get([FromQuery(Name = "number")] long number)
    {
        ulong lastItem = (ulong)number;
        ulong fact = 1;
        for (ulong i = 1; i < lastItem; i++)
        {
            fact = fact * i;
        }
        return fact.ToString();
    }