What is the sum of the digits of the base $7$ representation of $777_{10}$?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
What is the sum of the digits of the base $7$ representation of $777_{10}$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
9
What is the sum of the digits of the base $7$ representation of $777_{10}$?
train