21470639 has 4 divisors (see below), whose sum is σ = 21487056. Its totient is φ = 21454224.

The previous prime is 21470629. The next prime is 21470641. The reversal of 21470639 is 93607412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21470639 - 2⁴ = 21470623 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 (21470629) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6059 + ... + 8924.

It is an arithmetic number, because the mean of its divisors is an integer number (5371764).

Almost surely, 2^21470639 is an apocalyptic number.

21470639 is a deficient number, since it is larger than the sum of its proper divisors (16417).

21470639 is a wasteful number, since it uses less digits than its factorization.

21470639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16416.

The product of its (nonzero) digits is 9072, while the sum is 32.

The square root of 21470639 is about 4633.6420880340. The cubic root of 21470639 is about 277.9382529391.

The spelling of 21470639 in words is "twenty-one million, four hundred seventy thousand, six hundred thirty-nine".