A disarium number equals the sum of its digits each raised to the power of that digit's position. So \(89 = 8^1 + 9^2 = 8 + 81\), and \(135 = 1^1 + 3^2 + 5^3 = 1 + 9 + 125\). The multi-digit ones are 89, 135, 175, 518, 598, 1306, 1676, 2427, 2646798.
They're a positional cousin of the [[narcissistic]] (Armstrong) numbers, which raise every digit to the same power (the digit count) rather than to its position. Like most digit-power properties, the list is finite because the maximum possible sum eventually can't keep up with the number's size.