21604439 has 2 divisors, whose sum is σ = 21604440. Its totient is φ = 21604438.

The previous prime is 21604421. The next prime is 21604469. The reversal of 21604439 is 93440612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21604439 - 2¹² = 21600343 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21604469) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10802219 + 10802220.

It is an arithmetic number, because the mean of its divisors is an integer number (10802220).

Almost surely, 2^21604439 is an apocalyptic number.

21604439 is a deficient number, since it is larger than the sum of its proper divisors (1).

21604439 is an equidigital number, since it uses as much as digits as its factorization.

21604439 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 29.

The square root of 21604439 is about 4648.0575512788. The cubic root of 21604439 is about 278.5144064997.

The spelling of 21604439 in words is "twenty-one million, six hundred four thousand, four hundred thirty-nine".