How to declare variable for a function with other variable?

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n=var("n")
def T(n):
    a=1
    b=x
    if n==0:
        return a
    if n==1:
        return b
    else:
        for i in [2..n]:
            b=2*x*b-a
            a=(a+b)/(2*x)
    return b

Could you help me to compute T(i) at x=1 or anything ?Mean that I want to declare x is a variable of T(i), but I can't. Thank you so much