127 is the natural number following 126 and preceding 128.

In mathematics

One hundred twenty-seven is a Mersenne prime, 2⁷ - 1, and as such, in binary it is a repunit prime, a permutable prime and a palindromic prime. This also means it is the largest integer that can be represented by a signed byte. As a Mersenne prime, 127 is related to the perfect number 8128, and 2¹²⁷ - 1 is also a Mersenne prime, making it a double Mersenne prime. 127 is also a cuban prime of the form p = (x³ - y³) / (x - y), x = y + 1.

127 is a centered hexagonal number.

It is the 7th Motzkin number.

It is a nice Friedman number in base 10, since 127 = -1 + 2⁷, as well as binary since 1111111 = (1 + 1)¹¹¹ - 1 * 1.

In other fields

One hundred twenty-seven is also:

• ASCII and Unicode code point for delete.
• The number of provinces ruled by King Xerxes I, "from India to Ethiopia" (Holy Bible, Esther 1:1).
• The number of sons of Bethlehem at the Census of men of Israel upon return from exile (Holy Bible, Ezra 2:21).
• The year AD 127 or 127 BC.