In number theory, a balanced prime is a prime number with equal-sized prime gaps above and below it, so that it is equal to the arithmetic mean of the nearest primes above and below. Or to put it algebraically, given a prime number , where n is its index in the ordered set of prime numbers,
For example, 53 is the sixteenth prime; the fifteenth and seventeenth primes, 47 and 59, add up to 106, and half of that is 53; thus 53 is a balanced prime.
The first few balanced primes are
It is conjectured that there are infinitely many balanced primes.
Three consecutive primes in arithmetic progression is sometimes called a CPAP-3. A balanced prime is by definition the second prime in a CPAP-3. As of 2014[update] the largest known CPAP-3 has 10546 digits and was found by David Broadhurst. It is:
The value of n (its rank in the sequence of all primes) is not known.
The balanced primes may be generalized to the balanced primes of order n. A balanced prime of order n is a prime number that is equal to the arithmetic mean of the nearest n primes above and below. Algebraically, given a prime number , where k is its index in the ordered set of prime numbers,
Thus, an ordinary balanced prime is a balanced prime of order 1.The sequences of balanced primes of orders 2, 3, and 4 are given as (sequence A082077 in the OEIS), (sequence A082078 in the OEIS), and (sequence A082079 in the OEIS) respectively.
- Strong prime, a prime that is greater than the arithmetic mean of its two neighboring primes
- The Largest Known CPAP's. Retrieved on 2014-06-13.