21931709 has 2 divisors, whose sum is σ = 21931710. Its totient is φ = 21931708.

The previous prime is 21931703. The next prime is 21931711. The reversal of 21931709 is 90713912.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19829209 + 2102500 = 4453^2 + 1450^2 .

It is a cyclic number.

It is not a de Polignac number, because 21931709 - 2¹² = 21927613 is a prime.

Together with 21931711, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21931703) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965854 + 10965855.

It is an arithmetic number, because the mean of its divisors is an integer number (10965855).

Almost surely, 2^21931709 is an apocalyptic number.

It is an amenable number.

21931709 is a deficient number, since it is larger than the sum of its proper divisors (1).

21931709 is an equidigital number, since it uses as much as digits as its factorization.

21931709 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3402, while the sum is 32.

The square root of 21931709 is about 4683.1302565699. The cubic root of 21931709 is about 279.9137021467.

The spelling of 21931709 in words is "twenty-one million, nine hundred thirty-one thousand, seven hundred nine".