This site is supported by donations to The OEIS Foundation.

# Unit fractions

A unit fraction is a fraction having a numerator of 1. For example, ${\displaystyle \scriptstyle {\frac {1}{7}}}$ is a unit fraction.

## Problems involving unit fractions

There are various problems in number theory involving unit fractions.

### Smallest k such that 1/k can be written as a sum of exactly 2 unit fractions in n ways

The smallest integer ${\displaystyle \scriptstyle k}$ such that ${\displaystyle \scriptstyle {\frac {1}{k}}}$ can be written as a sum of two unit fractions in exactly ${\displaystyle \scriptstyle n}$ ways is given by

{1, 2, 4, 8, 6, 32, 64, 12, 256, 512, 24, 2048, 36, 30, 16384, 32768, 96, 72, 262144, 192, 1048576, 2097152, 60, 8388608, 216, 768, 67108864, 288, 1536, 536870912, ...} (A016017)

### Erdős-Straus conjecture

The Erdős-Straus conjecture says that

${\displaystyle {\frac {4}{n}}={\frac {1}{a}}+{\frac {1}{b}}+{\frac {1}{c}}}$

always has solutions in integers.