6.1. The two formulae at s = 1
Let \theta be a non-trivial Dirichlet character of conductor N, and let
\varepsilon_N be a primitive N-th root of unity.
(i) Classical value at s=1. We have
L(\theta,1) = -\frac{1}{G(\theta^{-1})}\sum_{c\in(\Z/N\Z)^\times}\theta^{-1}(c)\,\log\!\big(1-\varepsilon_N^{\,c}\big).
(ii) p-adic value at s=1. We have
L_p(\theta,1) = -\big(1-\theta(p)p^{-1}\big)\frac{1}{G(\theta^{-1})}\sum_{c\in(\Z/N\Z)^\times}\theta^{-1}(c)\,\log_p\!\big(1-\varepsilon_N^{\,c}\big).
Part (i) rests on the special-value description of Definition 2.1.3.
Part (ii) concerns the value at s=1 of the Definition 4.3.2 p-adic
L-function, which lies outside the range of the Theorem 5.1.1,
and is computed from the measures Definition 4.1.4.
The two formulae are identical up to replacing the complex logarithm \log by
its p-adic avatar \log_p and inserting the missing Euler factor at p,
namely (1-\theta(p)p^{-1}). If \theta is odd, both sides of the p-adic
formula vanish.