MATLAB: Line 21 giving me troubles – Math Solves Everything

Could someone help please? Having errors with line 21 for "Time". 
%This program will calculate the approximate time for electrons to travel 
% from cathode to anode of a rectifier tube.
%







clear
clc
%Get user input
min_V=input('Enter the min limit of accelerating voltage:');
max_V=input('Enter the max limit of accelerating voltage:');
r1=input('Enter the radius of the inner tube (cathode) in mm:');
r2=input('Enter the radius of the outer tube (anode) in mm:');
%
%
V=(min_V:1:max_V);
%Range of voltage 1-10, increments 1
z=log(r2./r1);
%Natural Logarithm of R2/R1
q=1.60206*10^-19;
%Charge of electron in coulombs
m=9.1083*10^-31;
%Mass of electron in kilograms
time=z*r1*(sqrt((2*m)/(q.*V)))*(1+(z/3)+(z^2/10)+(z^3/42)+(z^4/216));
%Time for electron to travel from cathode to anode (in sec)
%
%
%
%
%Display output as required
my_results=[V',time'];
disp('         ');
disp('Voltage Time');
disp('-------- ------');
disp('(volts)  (seconds)');
disp(my_results);
%
%End of file
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