# Brun's Theorem

## Theorem

The sum of the reciprocals of all the twin primes converges.

## Source of Name

This entry was named for Viggo Brun.

## Historical Note

While Brun's Theorem proves that the sum of the reciprocals of all the twin primes converges, it has not yet been established what it actually converges to.

The number, whatever it is, is referred to as Brun's constant. Its best estimate is updated as and when the occasion demands.

As pointed out by David Wells in his Curious and Interesting Numbers of $1986$:

Its value is exceedingly hard to calculate.