16
the simplest way to evaluate is to substitute n = 1, 2, 3, 4 into the expression and sum the terms
= [(2 × 1) - 1 ] + [(2 × 2) - 1 ] + [(2 × 3) - 1] + [(2 × 4) - 1]
= 1 + 3 + 5 + 7 = 16
