
    Given a maximum passenger capacity threshold, analyze bus route pairs where the sum of all factors (excluding the route number itself) of one route equals the other route number and vice versa, then calculate the total sum of all such paired routes up to the threshold. These paired routes represent optimal candidates for passenger load balancing in the transit network to minimize overcrowding.
    

    
def amicable_numbers_sum(limit):
    """
    Given a maximum passenger capacity threshold, analyze bus route pairs where the sum of all factors (excluding the route number itself) of one route equals the other route number and vice versa, then calculate the total sum of all such paired routes up to the threshold. These paired routes represent optimal candidates for passenger load balancing in the transit network to minimize overcrowding.
    

    """
def amicable_numbers_sum(limit):
    """
    Given a maximum passenger capacity threshold, analyze bus route pairs where the sum of all factors (excluding the route number itself) of one route equals the other route number and vice versa, then calculate the total sum of all such paired routes up to the threshold. These paired routes represent optimal candidates for passenger load balancing in the transit network to minimize overcrowding.
    

    """
    if not isinstance(limit, int):
        return 'Input is not an integer!'
    if limit < 1:
        return 'Input must be bigger than 0!'
    amicables = set()
    for num in range(2, limit + 1):
        if num in amicables:
            continue
        sum_fact = sum([fact for fact in range(1, num) if num % fact == 0])
        sum_fact2 = sum([fact for fact in range(1, sum_fact) if sum_fact % fact == 0])
        if num == sum_fact2 and num != sum_fact:
            amicables.add(num)
            amicables.add(sum_fact2)
    return sum(amicables)