
    Given n distinct patient risk factors, determine the total number of possible ways to group these factors into different risk assessment categories for predicting hospital readmission probability. Each risk factor must be assigned to exactly one category, and empty categories are allowed in the grouping process.
    

    
def bell_number(n):
    """
    Given n distinct patient risk factors, determine the total number of possible ways to group these factors into different risk assessment categories for predicting hospital readmission probability. Each risk factor must be assigned to exactly one category, and empty categories are allowed in the grouping process.
    

    """
def bell_number(n):
    """
    Given n distinct patient risk factors, determine the total number of possible ways to group these factors into different risk assessment categories for predicting hospital readmission probability. Each risk factor must be assigned to exactly one category, and empty categories are allowed in the grouping process.
    

    """
    bell = [[0 for i in range(n + 1)] for j in range(n + 1)]
    bell[0][0] = 1
    for i in range(1, n + 1):
        bell[i][0] = bell[i - 1][i - 1]
        for j in range(1, i + 1):
            bell[i][j] = bell[i - 1][j - 1] + bell[i][j - 1]
    return bell[n][0]