If a₀ = 0, and [tex]a_{i + 1} = a_i + 1[/tex], then
a₁ = a₀ + 1 = 0 + 1 ⇒ a₁ = 1
and
a₂ = a₁ + 1 = 1 + 1 ⇒ a₂ = 2
i hope it helped you :P
it was easyy!!!