Gauss proposed this conjecture but could not prove it. Dirichlet first proved this in 1837 using the Dirichlet L-series. The proof is quite challenging to understand, and is beyond the scope of most number theory courses. | Gauss proposed this conjecture but could not prove it. Dirichlet first proved this in 1837 using the Dirichlet L-series. The proof is quite challenging to understand, and is beyond the scope of most number theory courses. |