26 Two sequences have 1, 3, 5 as their first three terms. (a) In the first sequence, each term is 2 more than the term before it. (i) Find an expression, in terms of n, for the nth term. (ii) The kth term of this sequence is 841. Find the value of k. (b) The nth term of the second sequence is 2^n-1 - (n-1)(n-4)/2. (i) Find the fourth term of this sequence. (ii) Find the fifth term of this sequence.