×

Hello! Socratic's Terms of Service and Privacy Policy have been updated, which will be automatically effective on October 6, 2018. Please contact hello@socratic.com with any questions.

How can I write the symbol of ”combinations of #n# things taken #k# at a time”?

I am familiar with the notation #C_n^k#, but I noticed that most people on Socratic use this kind of notation: i.imgur.com