Calculate the sum of the series: 1 + 2 + 3 + ... + 81 + 82 + 81 + ... + 3 + 2 + 1.

The digits of a three-digit number taken in order are in geometric progression. If 1 is added to the middle digit, they form an arithmetic progression. If 594 is subtracted from the number, a new number with the same digits in reverse order is formed. The original number is divisible by which of the following numbers?

Find the sum of the series: 128 + 136 + 145 + 155 + ... + 14950.