How many possible pairs can be made from the 26 regional indicator symbols? The answer is 676.
Regional indicator symbols are 26 Unicode characters corresponding to the letters A through Z. Emoji flag sequences generally combine two of them in a specific order, mirroring two-letter country codes. Because each position can contain any of 26 symbols, the calculation is 26 × 26 = 676 possible ordered pairs.
That mathematical total includes combinations that are not assigned to countries, as well as repeated pairs such as AA. It describes the number of possible two-symbol sequences, not the number of currently recognized national flags. A common mistake is to calculate only combinations of two different symbols: that produces 325, but it ignores order and repeated symbols. AB and BA are different sequences.
Regional indicator symbols were added to Unicode 6.0 as a way to encode country flags without creating a separate character for every flag. Their practical use is governed by valid ISO 3166-1 alpha-2 codes, so only a subset of the 676 theoretical pairs normally renders as recognized national flags.