21979439 has 2 divisors, whose sum is σ = 21979440. Its totient is φ = 21979438.

The previous prime is 21979429. The next prime is 21979457. The reversal of 21979439 is 93497912.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21979439 - 2⁴ = 21979423 is a prime.

It is a Sophie Germain prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21979439.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21979429) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989719 + 10989720.

It is an arithmetic number, because the mean of its divisors is an integer number (10989720).

Almost surely, 2^21979439 is an apocalyptic number.

21979439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21979439 is an equidigital number, since it uses as much as digits as its factorization.

21979439 is an evil number, because the sum of its binary digits is even.

The product of its digits is 122472, while the sum is 44.

The square root of 21979439 is about 4688.2234375081. The cubic root of 21979439 is about 280.1166138411.

The spelling of 21979439 in words is "twenty-one million, nine hundred seventy-nine thousand, four hundred thirty-nine".