21252639 has 8 divisors (see below), whose sum is σ = 29251072. Its totient is φ = 13711320.

The previous prime is 21252617. The next prime is 21252653. The reversal of 21252639 is 93625212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21252639 - 2⁵ = 21252607 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21252139) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 114169 + ... + 114354.

It is an arithmetic number, because the mean of its divisors is an integer number (3656384).

Almost surely, 2^21252639 is an apocalyptic number.

21252639 is a deficient number, since it is larger than the sum of its proper divisors (7998433).

21252639 is a wasteful number, since it uses less digits than its factorization.

21252639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 228557.

The product of its digits is 6480, while the sum is 30.

The square root of 21252639 is about 4610.0584594992. The cubic root of 21252639 is about 276.9943783695.

The spelling of 21252639 in words is "twenty-one million, two hundred fifty-two thousand, six hundred thirty-nine".