Respuesta :

altavistard

Answer:

21

Step-by-step explanation:

Try using this notation:  a(n)     and not    an.

an=n^3-2n becomes    a(n) = n^3 - 2n.

Then a(1) = 1^3 - 2(1) = 1 - 2 = -1

         a(2) = 2^3 - 2(2) = 8 - 4 = 4

         a(3) = 3^3 - 2(3) = 27 - 6 = 21