how can i find the coefficient of this signal?

if i have this signal st = exp((10 - t) / 2);

Harmonic = 4;
n = (1:Harmonic);
T = 5;
f = 1/T;
t = linspace(0,T,500+1); % 5 cycles
t = t(1:end-1);
st = exp((10 - t) / 2);

how can i find a0, an, bn for four harmonics and plot the graph for 5 cycles? without using int and syms

[Birdman]

Where is a0, an, bn in the equation ?

[ocsse]

question's updated