Олимпиадный тренинг

Задача 39088. Let's count the numbers - 10


The value of an arithmetic expression
\(3 \cdot 7^{112} - 2\cdot7 ^{78}+4\cdot7^{63}- 2 \cdot 7^{35}-7^{8} -52\)
written in the number system with base 7. How many significant digits of 0  does this entry contain?