> Is that common $6$ in the denominator the tip of the ice berg of a direct connection between them?
Yes. See Bernoulli numbers. In particular, the values of $\zeta(2n)$, as well the Faulhaber's formulas for
the sums of _k_ -th powers of the first _n_ natural numbers, depend on them. In this case, $B_2=\dfrac16$