base36

Base36 is a positional numeral system that uses 36 distinct symbols to represent integers. The standard symbol set consists of the decimal digits 0 through 9 and the letters A through Z, representing values 0–35. Each position in a base-36 number corresponds to a power of 36, with the rightmost digit representing 36^0, the next 36^1, and so on.

In practice, base-36 strings are commonly written using uppercase letters, though some contexts allow lowercase and treat the representation as case-insensitive. The exact symbol set and case handling can vary by implementation, but the underlying value is defined by the 0–35 mapping.

Encoding and decoding between decimal and base-36 follow standard base-conversion rules. To encode from decimal to base-36, repeatedly divide by 36 and record the remainders, mapping remainders 0–9 to '0'–'9' and 10–35 to 'A'–'Z'. To decode, sum the values of each digit times 36 raised to the power of its position. Negative integers are typically represented with a leading minus sign.

Base-36 offers more compact representations than decimal for large numbers, while remaining readable and relatively easy to type. It is not designed for cryptographic security or collision resistance, so it should not be used for secure identifiers. Common applications include compact human-readable IDs for databases, order or coupon codes, short URLs, and other contexts where a denser alphanumeric key is desirable. Some systems also use variants with lowercase letters or mixed-case handling, which can affect readability and sorting but do not change the underlying numerical value.