20731309 has 2 divisors, whose sum is σ = 20731310.
Its totient is φ = 20731308.
The previous prime is 20731307. The next prime is 20731327. The reversal of 20731309 is 90313702.
It is a weak prime.
It can be written as a sum of positive squares in only one way, i.e., 19554084 + 1177225 = 4422^2 + 1085^2
It is a cyclic number.
It is not a de Polignac number, because 20731309 - 21 = 20731307 is a prime.
Together with 20731307, it forms a pair of twin primes.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (20731301) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10365654 + 10365655.
It is an arithmetic number, because the mean of its divisors is an integer number (10365655).
Almost surely, 220731309 is an apocalyptic number.
It is an amenable number.
20731309 is a deficient number, since it is larger than the sum of its proper divisors (1).
20731309 is an equidigital number, since it uses as much as digits as its factorization.
20731309 is an evil number, because the sum of its binary digits is even.
The product of its (nonzero) digits is 1134, while the sum is 25.
The square root of 20731309 is about 4553.1647235741.
The cubic root of 20731309 is about 274.7106996191.
The spelling of 20731309 in words is "twenty million, seven hundred thirty-one thousand, three hundred nine".