Time complexity for dependant nested for loop?

Question

Can you explain me how to find time complexity for this?

sum=0;
for(k=1;k<=n;k*=2)
  for(j=1;j<=k;j++)
     sum++;

So, i know the out

Answer 1

I believe you should proceed like the following to formally obtain your algorithm's order of growth complexity, using Mathematics (Sigma Notation):