
    Design a function that calculates the total number of bus route transfer points at a given hierarchical planning level, where each level builds upon previous levels by adding interconnected transfer points in a pyramidal structure. The total number of transfer points at level n represents the cumulative sum of points from all levels up to and including level n, forming a tetrahedral pattern of route connectivity.
    

    
def tetrahedral_number(n):
    """
    Design a function that calculates the total number of bus route transfer points at a given hierarchical planning level, where each level builds upon previous levels by adding interconnected transfer points in a pyramidal structure. The total number of transfer points at level n represents the cumulative sum of points from all levels up to and including level n, forming a tetrahedral pattern of route connectivity.
    

    """
def tetrahedral_number(n):
    """
    Design a function that calculates the total number of bus route transfer points at a given hierarchical planning level, where each level builds upon previous levels by adding interconnected transfer points in a pyramidal structure. The total number of transfer points at level n represents the cumulative sum of points from all levels up to and including level n, forming a tetrahedral pattern of route connectivity.
    

    """
    return n * (n + 1) * (n + 2) / 6