The reason is that ‘t’ needs a subscript:
x(n+1) = x(n) + h * ((8*(x(n))/(t(n)+1))-(t+1)*(x(n)^2));
↑ ← HERE
so:
x(n+1) = x(n) + h * ((8*(x(n))/(t(n)+1))-(t(n)+1)*(x(n)^2));
works.
Using ‘t’ without a subscript uses the entire vector. Using ‘t’ with a subacript uses only that one element.