For each, find an appropriate function.

(a) Find a function $f(k)$ such that $$1 + 2 + \dots + 25 = \sum\limits_{k=1}^{25} f(k).$$ $f(k)$ =

(b) Find a function $g(k)$ such that $$5 + 7 + 9 + 11 + 13 = \sum\limits_{k=0}^{4} g(k).$$ $g(k)$ =