The terms of a sequence {a_n} are given by the formula

a_n = n² - n +5, where n = 1, 2, 3, 4, ...

Two different terms are picked at random from 

(i) the first 10 terms

(ii) the first 100 terms

(iii) the first 10m terms, where m is some integer

(iv) all the terms in the series

In each case, what is the probability that the two terms chosen differ by a multiple of 10?