21391679 has 4 divisors (see below), whose sum is σ = 22321776. Its totient is φ = 20461584.

The previous prime is 21391651. The next prime is 21391703. The reversal of 21391679 is 97619312.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21391679 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391619) 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, 465014 + ... + 465059.

It is an arithmetic number, because the mean of its divisors is an integer number (5580444).

Almost surely, 2^21391679 is an apocalyptic number.

21391679 is a deficient number, since it is larger than the sum of its proper divisors (930097).

21391679 is an equidigital number, since it uses as much as digits as its factorization.

21391679 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 930096.

The product of its digits is 20412, while the sum is 38.

The square root of 21391679 is about 4625.1139445423. The cubic root of 21391679 is about 277.5971209979.

The spelling of 21391679 in words is "twenty-one million, three hundred ninety-one thousand, six hundred seventy-nine".