Let $B \ge 2$ be integer and $[x]$ denote the nearest integer to real $x$.
For $2 \le B \le 10^5$ computations with mpmath suggest:
$$ [\zeta(1-1/B)]=-B+1 \qquad (1)$$
Is (1) true for all $B \ge 2$?
Let $B \ge 2$ be integer and $[x]$ denote the nearest integer to real $x$.
For $2 \le B \le 10^5$ computations with mpmath suggest:
$$ [\zeta(1-1/B)]=-B+1 \qquad (1)$$
Is (1) true for all $B \ge 2$?
We can make the error mentioned by Wojowu in his comment explicit by using some results on the Laurent coefficients of the zeta function. There are a few results on this, but I'll just use Theorem 2 of this paper by Berndt (which gives a more general result for the Hurwitz zeta function). The relevant result is
Theorem. (Berndt) Write $$ \zeta(s) = \frac{1}{s-1} + \sum_{n=0}^\infty \gamma_n (s-1)^n $$ for the Laurent series expansion of $\zeta$ around $s=1$. Then for $n\geq 1$, we have $$ \left|\gamma_n\right| \leq \frac{4}{n\pi^n}. $$ For $B\geq 2$ an integer, write $$ \zeta\left(1-\frac{1}{B}\right) = -B + \gamma + R(B), $$ where $\gamma=\gamma_0\approx .577...$ is the usual Euler-Mascheroni constant and $$ R(B) = \sum_{n=1}^\infty \gamma_n \left(-\frac{1}{B}\right)^n. $$ Applying the triangle inequality and Berndt's result, we have $$ \left|R(B)\right| \leq \sum_{n=1}^\infty \frac{4}{n(B\pi)^n} \leq \frac{4}{B}\sum_{n=1}^{\infty} \frac{1}{n\pi^n}. $$ The sum on the right converges rapidly and is numerically $\approx 0.383...$. Thus $$ \left| R(B) \right| \leq \frac{2}{B}. $$ (By a more careful analysis, the constant 2 can be replaced with 1.) For $B \geq 26$, it follows that $$ \frac{1}{2} < \gamma+ R(B) < 1. $$ Therefore $$ \left[ \zeta\left(1-\frac{1}{B} \right) \right] = -B+1 $$ for $B \geq 26$. The remaining cases can be verified via computer.