sixtysix

Sixtysix, typically written as sixty-six or sixtysix, is the integer that follows sixty-five and precedes sixty-seven. In decimal notation it is 66. It can be represented in other numeral systems as 1000010 in binary, 0x42 in hexadecimal, and 102 in octal. The digits sum to 12, giving a digital root of 3. It is an even, composite number with prime factorization 2 × 3 × 11.

In mathematics, 66 is a triangular number, equal to the sum of the integers 1 through 11 (11 × 12 / 2 = 66). It is also a hexagonal number, specifically the sixth in the sequence defined by n(2n−1). These properties place 66 in several figurate-number sequences and relate to its symmetry and divisibility characteristics.

The number appears in various cultural and practical contexts. Route 66, known as the historic U.S. highway connecting Chicago and Los Angeles, is one of the most famous uses of the numeral and has a prominent place in American popular culture. The year 66 CE is noted for events surrounding the early stages of the First Jewish–Roman War. The country calling code +66 is assigned to Thailand, and in computing contexts, the ASCII code for the capital letter B is 66.

The 66th day of the year falls on March 7 in common years and March 6 in leap years. The term sixtysix is also encountered in branding, media, and numerical references where the exact value is required without hyphenation.