“Perhaps the prettiest number system of all,” writes Donald E. Knuth in The Art of Computer Programming, “is the balanced ternary notation.” As in ordinary ternary numbers, the digits of a balanced ternary numeral are coefficients of powers of 3, but instead of coming from the set {0, 1, 2}, the digits are –1, 0 and 1. They are “balanced” because they are arranged symmetrically about zero. For notational convenience the negative digits are usually written with a vinculum, or overbar, instead of a prefixed minus sign, but here the vinculum is shown as an overstrike, thus: 1.

...What makes balanced ternary so pretty? It is a notation in which everything seems easy. Positive and negative numbers are united in one system, without the bother of separate sign bits. Arithmetic is nearly as simple as it is with binary numbers; in particular, the multiplication table is trivial. Addition and subtraction are essentially the same operation: Just negate one number and then add. Negation itself is also effortless: Change every 1 into a 1, and vice versa. Rounding is mere truncation: Setting the least-significant trits to 0 automatically rounds to the closest power of 3.