| APA | 21CN. (2012, February 11). In Acronym Geek. Retrieved 19:52, February 11, 2012, from http://www.acronymgeek.com/21CN |
| MLA | "21CN." Acronym Geek. (2012). Acronym Geek. 11 Feb 2012 <http://www.acronymgeek.com/21CN>. |
| MHRA | '21CN', Acronym Geek, 11 February 2012, <http://www.acronymgeek.com/21CN> [accessed 11 February 2012] |
| Chicago | "21CN", http://www.acronymgeek.com/21CN (accessed February 11, 2012). |
| CBE/CSE | 21CN [Internet]. Acronym Geek; 2012 Feb 11 [cited 2012 Feb 11]. Available from: http://www.acronymgeek.com/21CN. |
| Bluebook | 21CN, http://www.acronymgeek.com/21CN (last visited February 11, 2012). |
| Bluebook: Harvard JOLT | See Acronym Geek, 21CN, http://www.acronymgeek.com/21CN (optional description here) (as of Feb. 11, 2012, 19:52). |
| AMA | 21CN. Acronym Geek. February 11, 2012, 19:52. Available at: http://www.acronymgeek.com/21CN. Accessed February 11, 2012, 19:52. |