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A hexavigesimal numeral system has a base of twenty-six.

Base-26 may be represented by using conventional numerals for the digits 0 to 9, and then the letters A to P for the tenth to twenty-fifth digits. "10" would represent 26, "11" = 27, "AB" = 271, and "NP" = 623.

Alternatively, base-26 may be represented using only letters of the Basic Latin alphabet. As there are 26 letters in English, base-26 is also the highest base in which this is possible without being case-sensitive and hence utilizes every letter. 0 is represented by A, 1 = B, 2 = C ... 24 = Y, and 25 = Z. For example: 26 = BA; 678 = BAC.

The most common everyday use of the hexavigesimal system is to identify columns on spreadsheet programs such as Microsoft Excel. Otherwise, these systems are of limited practical value, although letters used in nominal or serial numbers can be thought as hexavigesimal numerals for calculation purposes if the entire alphabet is used.


The fact that 26 is a composite number and lies between two composite numbers (25 and 27) leads to many simple fractions.

B/C = A.N
B/E = A.GN

The fractions B/G, B/I, B/J, B/K, B/M, B/N, B/P, B/Q are also simple.

Conversion algorithm (alphabet-only system)[edit]

Any number may be converted to base-26 by repeatedly dividing the number by 26. The remainders of each division will be the base-26 digits from right to left (least-significant to most-significant place). For example, to convert 678 to "BAC", the first division yields 26 remainder 2, so 2 (C) is the last digit. The quotient 26 is divided again, yielding 1 remainder 0, so 0 (A) is the second-last digit. The next quotient 1 is then divided to give 0 remainder 1, so the final digit is 1 (B). This is extensible to fractions.

This algorithm may be represented in Java to convert a non-negative integer to a base-26 character string as follows:

    public static String toBase26(int number){
        number = Math.abs(number);
        String converted = "";
        // Repeatedly divide the number by 26 and convert the
        // remainder into the appropriate letter.
        while (number > 0)
            int remainder = number % 26;
            converted = (char)(remainder + 'A') + converted;
            number = (number - remainder) / 26;
        return converted;

The reverse conversion is achieved by processing each base-26 digit from left to right. The value of the first (leftmost) digit is multiplied by 26 and then added to the subsequent digit. If digits remain, then the cumulative sum is multiplied by 26 before adding the next digit, and so on. Note that this works for any base as long as one has the tools to perform multiplication by 26 and addition in that base. For example, to convert "BAC" to 678, B (1) is multiplied to give 26 and added to A (0) to yield 26. This is multiplied to give 676 and added to C (2) to yield 678.

The reverse conversion algorithm may be represented in Java to convert a base-26 character string to an integer as follows:

    public static int fromBase26(String number) {
        int s = 0;
        if (number != null && number.length() > 0) {
            s = number.charAt(0) - 'A';
            for (int i = 1; i < number.length(); i++) {
                s *= 26;
                s += number.charAt(i) - 'A';
        return s;

John Nash[edit]

While at Princeton University in the 1970s, mathematician John Nash worked extensively in base-26 as part of his obsession with numerology and the uncovering of "hidden" messages. Nash composed letters and other messages in which the actual English text also represented a base-26 equation, the answer to which would itself be both a base-26 number and a word or phrase in English. Nash is believed to have devised algorithms with which he was able to adapt primitive electronic calculators to assist him in performing hexavigesimal calculations.[1]

Bijective base-26[edit]

Using bijective numeration, it is possible to operate in base-26 without a zero; it uses the digits from "A" to "Z" to represent one to twenty-six and has no zero. Many spreadsheets including Microsoft Excel use the 26-adic counting system with the "digits" A-Z to label the columns of a spreadsheet, starting A, B, C... Z, AA, AB... AZ, BA... ZZ, AAA, etc. A variant of this system is used to name variable stars.[2]

The following algorithm (in Java) could be used to convert numbers from decimal to bijective base-26:

public static String toBase26(int n){
  StringBuffer ret = new StringBuffer();
    ret.append((char)('A' + n%26));
  return ret.reverse().toString();

The following algorithm (also in Java) could be used to convert numbers from bijective base-26 to decimal:

public static int fromBase26(String number){
  number = number.toUpperCase();
  int decimalValue = 0;
  for (int i = 0; i <  number.length(); i++) {
    decimalValue *= 26;
    decimalValue += (number.charAt(i) - 64);
  return decimalValue;


  1. ^ Nasar, Sylvia (2001). A Beautiful Mind. Simon and Schuster. pp. 333–6. ISBN 0-7432-2457-4. 
  2. ^ Levy, David H. (1998). Observing Variable Stars: A Guide for the Beginner. The practical astronomy handbook series 5. Cambridge University Press. pp. 34–35. ISBN 9780521627559. .