21739309 has 2 divisors, whose sum is σ = 21739310. Its totient is φ = 21739308.

The previous prime is 21739303. The next prime is 21739321. The reversal of 21739309 is 90393712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15093225 + 6646084 = 3885^2 + 2578^2 .

It is a cyclic number.

It is not a de Polignac number, because 21739309 - 2¹⁹ = 21215021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21739303) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10869654 + 10869655.

It is an arithmetic number, because the mean of its divisors is an integer number (10869655).

Almost surely, 2^21739309 is an apocalyptic number.

It is an amenable number.

21739309 is a deficient number, since it is larger than the sum of its proper divisors (1).

21739309 is an equidigital number, since it uses as much as digits as its factorization.

21739309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10206, while the sum is 34.

The square root of 21739309 is about 4662.5431901485. The cubic root of 21739309 is about 279.0927651516.

The spelling of 21739309 in words is "twenty-one million, seven hundred thirty-nine thousand, three hundred nine".