21364639 has 2 divisors, whose sum is σ = 21364640. Its totient is φ = 21364638.

The previous prime is 21364633. The next prime is 21364643. The reversal of 21364639 is 93646312.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21364639 - 2⁹ = 21364127 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21364633) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10682319 + 10682320.

It is an arithmetic number, because the mean of its divisors is an integer number (10682320).

Almost surely, 2^21364639 is an apocalyptic number.

21364639 is a deficient number, since it is larger than the sum of its proper divisors (1).

21364639 is an equidigital number, since it uses as much as digits as its factorization.

21364639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 23328, while the sum is 34.

The square root of 21364639 is about 4622.1898489785. The cubic root of 21364639 is about 277.4801067903.

The spelling of 21364639 in words is "twenty-one million, three hundred sixty-four thousand, six hundred thirty-nine".