In the first half of the lecture we will investigate the question which finite Galois extensions of Q have an abelian Galois group. In the second part we will see that the study of characters of such abelian Galois groups leads to interesting number theoretic results. For example, we will prove Chebotarev's density theorem for abelian extensions of Q. This allows us to answer the following question: How many prime numbers end in the digit 7 (or, say, in 2023)?

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