Fracional order transfer function

I tried to write a matlab script for the computation of this transfer function but I keep receving an error message saying that the exponent must a scalar integer.

How can I overcome this issue?

Thank you in advance.

In the following is reported the piece of code in question

s=tf('s');
v=20;
a=5;
denom=0; 
for k=1:v
    denom=denom+((s/a)^((k-1)/v));   
end
C=1/denom;

[Bandar]

Transfer function must be a ratio of polynomails but this is not the case in your question.

[Deepak Kumar]

Refer the below link for the answer:

https://www.mathworks.com/matlabcentral/answers/496431-fractional-order-transfer-function?s_tid=answers_rc1-1_p1_BOTH