Missing Number

Archaeologist John and his team have unearthed the remains of an ancient civilisation. The partially destroyed walls of its houses contain strange pairs of numbers. John assumes that the first number in each pair always corresponds to a base (itself written in base $10$) and the second number in that pair is written in this base ― for example, `3 2110` denotes $(2110)_3 = 2 \cdot 3^3 + 1 \cdot 3^2