Fourier expression for infinite recurring binary sequence

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We have infinite binary sequences of type $$\langle g_n \rangle_{j=4}=\{0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,1,...\} \,;\, n\to\infty$$ where $j$ indicates the length of a period.

we try to express them with a Fourier in a shape similar the spectrum:

$$G(x)=\sum_{k=1}^\infty a_k\,e^{(i\,2\pi\,k\,x / j)}$$

None of us is good in Fourier at all. May someone help us with the right expression.

Many thanks

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The inverse Fourier in its most elegant form is for such sequences:

$$G(x)=\sum_{k=-j}^j \frac{2 \pi}{j}\,e^{(i\,2\pi\,(k-1)\,x / j)}$$

while $i=\sqrt{-1}$ and angular frequency:

$$\omega_j=\frac{2 \pi}{j}$$