Thank you so much for your quick reply. I really appreciate it.

Hi! that's a lambda expression. You can read more about it here: https://en.cppreference.com/w/cpp/language/lambda or https://docs.microsoft.com/en-us/cpp/cpp/lambda-expressions-in-cpp?view=msvc-160

You so cool, thanks!: )

By the same reasoning, all Python solutions should get a comment saying that 'Good solution but requires Python. Would be a problem if writing for embedded devices'. This shows that this comment about C++11 is completely irrelevant.

Not trying to say you're wrong, but I believe this is what siebenschlaefer is trying to say.

Wow, never met accumulate before! )
Btw, is it as fast as a straightforward solution?

Thanks!

Great solution.
Minor improvement : You could put just '(1)' instead '(1+1)'