
    Given a delivery network that expands by creating hierarchical connections between zones, where each new zone forms route combinations with all existing zones in a tetrahedral pattern, determine the total number of possible route combinations when the network contains n zones. The number of route combinations follows a tetrahedral sequence, where each level builds upon previous levels to create an optimal distribution pattern for the delivery fleet.
    

    
def tetrahedral_number(n):
    """
    Given a delivery network that expands by creating hierarchical connections between zones, where each new zone forms route combinations with all existing zones in a tetrahedral pattern, determine the total number of possible route combinations when the network contains n zones. The number of route combinations follows a tetrahedral sequence, where each level builds upon previous levels to create an optimal distribution pattern for the delivery fleet.
    

    """
def tetrahedral_number(n):
    """
    Given a delivery network that expands by creating hierarchical connections between zones, where each new zone forms route combinations with all existing zones in a tetrahedral pattern, determine the total number of possible route combinations when the network contains n zones. The number of route combinations follows a tetrahedral sequence, where each level builds upon previous levels to create an optimal distribution pattern for the delivery fleet.
    

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