Put all of these numbers in a line...obviously, don't put ALL of them, but enough so you can see what you're doing. 1 + 2 + 3 + ... + 297,624,985 Now put all these numbers BACKWARDS underneath that. 1 + 2 + 3 + ... + 297,624,985 297,624,985 + 297,624,984 + 297,624,983 + ... + 1 Now add the first series to the second, and you'll see that they add up to: 297,624,986 + 297,624,986 + 297,624,986 + ...297,624,986 Since there were 297,624,985 terms, the total sum here is 297,624,986 * 297,624,985 But since you added it twice, you divide it by two: 148,812,493 * 297,624,985 This is 44,290,315,996,937,605, so...yes, it is MUCH larger.