The upper- and lowercase versions of the English alphabet combined with the ten single digits make up the list of alphanumeric characters. Thus, a list of traditional alphanumeric characters includes 62 characters: Aa, Bb, Cc, Dd, Ee, Ff, Gg, Hh, Ii, Jj, Kk, Ll, Mm, Nn, Oo, Pp, Qq, Rr, Ss, Tt, Uu, Vv, Ww, Xx, Yy, Zz, 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
There is some disagreement over the inclusion of punctuation marks in the alphanumeric designation. Non-English letters that may be included are the Roman é and ç and the thorn letter þ. Characters not typically included in an alphanumeric list include special symbols, such as @, #, $, and %. Underscores are sometimes considered part of the alphanumeric set.
When coding, some alphanumeric sets exclude letters that can be easily confused with numbers. For instance, airlines and auto manufacturers both skip the lowercase letter I to avoid confusion with the numeral 1. Auto manufacturers also skip O and Q to avoid confusion with the numeral 0. Other applications do not use the letter S because of its similarity to the numeral 5, or the letter Z because of its similarity to the numeral 2.