Hexadecimal uses sixteen symbols per place, mixing the usual digits with letters from a through f.

The longer version

Sixteen symbols per column means the alphabet has to be recruited once the usual ten digits run out, so a through f stand for ten through fifteen. Each column is therefore worth sixteen times the one on its right, and any byte maps neatly onto exactly two of them.

The match with binary is why it survives: four bits make one symbol, so translating between the two is a matter of memorising sixteen small groups rather than doing arithmetic. Long binary strings become short enough to read aloud without error. Programmers meet it in memory addresses, colour codes, and error values, where compactness beats decimal familiarity.

Where this entry sits

This section collects odd corners of mathematics, from stubborn prime numbers to counting systems older than modern schools. Expect famous constants, probability puzzles, shapes that break everyday intuition, and numbers far too large to picture. The full list sits on the Numbers and Math page, where every entry is listed in order.