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How should one refer to the practice of using letters instead of numbers for counting?

I'm referring to this:

"A, B, C, ... X, Y, Z, AA, AB, AC, AD, AE, AF, AG... ZX, ZY, ZZ, AAA, AAB..."

Microsoft Excel uses this notation for spreadsheet columns, but I'm unaware if there's a proper name for this. "Alphabetic numbering" sounds rather nebulous, but it's the closest I can think of.


UPDATE: Found the name with the help of FumbleFingers' answer; it's called bijective hexavigesimal or bijective base-26, a type of bijective numeration:

In the bijective base-26 system one may use the Latin alphabet letters "A" to "Z" to represent the 26 digit values one to twenty-six.

With this choice of notation, the number sequence (starting from 1) begins A, B, C, ..., X, Y, Z, AA, AB, AC, ..., AX, AY, AZ, BA, BB, BC, ...

Each digit position represents a power of twenty-six, so for example, the numeral ABC represents the value 1\times 26^2 + 2\times 26^1 + 3\times 26^0.

"Hexavigesimal" itself seems to refer to any numbering system that uses a radix of 26, rather than one that uses strictly alphabetic characters alone. So while it wasn't quite correct, it put me on the right path.

  • This is a good question. I'm not sure that there is a name for it. Counting with letters preceded counting with numbers. Anciently, whether it be the Greeks, the Hebrews or the Egyptians, peoples' letters were also their numbers. The Romans were a bit of an aberration because these others used A(α,א,..) for 1, B(β,ב,..) for 2, etc. It wasn't until the adoption of Arabic numbers that numbers became different than letters. It often becomes the case that the original form of something, the way it was originally done, has no name, only the innovation, the new way gets a name. – Benjamin Harman Jan 17 '16 at 13:48
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    You should know that "bijective" adjectivally refers to associating two sets in such a way that every member of each set is uniquely paired with a member of the other set. If one set is numbers and the other set is letters, then that would be bijective. However, bijective isn't limited to numbers. For example, if one set is John, Mary, and George, and another set is red, green, and blue, and you uniquely associate John with red, Mary with green, and George with blue, that is a bijective association. It has nothing to do with numbers but only associating two sets in such a manner. – Benjamin Harman Jan 17 '16 at 13:59
  • @BenjaminHarman Aye, but when mentioning "bijective base-𝐾", it makes it clear the topic is numerical in nature. The added information is interesting though, thank you. =) – user45483 Jan 17 '16 at 14:03
  • Bijective only describes the assignment. In mathematics and linguistics, that method would be described as shortlex and the use of letters would be called lexicographcial. You can look both of these terms up in any textbook and probably in Wikipedia. None of these adjectives are a noun, though. They are not a name for the method, which is what you asked for. – Benjamin Harman Jan 17 '16 at 14:09
  • I really don't see the relevance of bijective to this context. I'm also somewhat dubious as to the merits of the recent update to the question text. – FumbleFingers Jan 17 '16 at 14:10
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According to Wikipedia, the "pseudo-technical" term is hexavigesimal. But you probably won't find that in a dictionary. Most people just refer to base 26 Alphabet Numbers

  • Perfect! Googling "hexavigesimal" brought up a related SO question, where a user namedropped "Bijective Hexavigesimal", a type of bijective numeration. – user45483 Jan 17 '16 at 13:35
  • @Alhadis: Actually, I used to use base 36 a lot in my programming days (it's an easy way to represent large numbers in short form using the common "digit" symbols 0-9, A-Z). But I certainly never used Wikipedia's hexatrigesimal - all my inline comments referred to the format as radix 36. So although it's true that most people just refer to your one as base 26, I personally would have called that radix 26 if I'd had any real need for a term. – FumbleFingers Jan 17 '16 at 14:05
  • Basically, I wrote a JavaScript function to convert a number to its "alphabetically-indexed" counterpart. Trouble is, I had no idea what to name it, and base-26 didn't make it obvious enough that numbers were not included in the result. It also made me wonder if there was a more formal description for what I was thinking of. – user45483 Jan 17 '16 at 14:16
  • @Alhadis: oic. Well, you could have saved yourself the bother by looking at How to create a function that converts a Number to a Bijective Hexavigesimal?, asked on SO several years ago. But at least I can now see where bijective comes into play - it just means adding 65 to each "digit" to get the ascii code of an upper-case letter for i/o purposes. – FumbleFingers Jan 17 '16 at 14:24
  • I enjoy challenging myself with writing code from scratch without Googling for answers. This is how archnerds like myself spend their Sunday evenings, heh. – user45483 Jan 17 '16 at 14:25

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