21239915 has 4 divisors (see below), whose sum is σ = 25487904. Its totient is φ = 16991928.

The previous prime is 21239903. The next prime is 21239917. The reversal of 21239915 is 51993212.

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 21239915 - 2⁴ = 21239899 is a prime.

It is a super-2 number, since 2×21239915² = 902267978414450, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21239917) 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, 2123987 + ... + 2123996.

It is an arithmetic number, because the mean of its divisors is an integer number (6371976).

Almost surely, 2^21239915 is an apocalyptic number.

21239915 is a deficient number, since it is larger than the sum of its proper divisors (4247989).

21239915 is an equidigital number, since it uses as much as digits as its factorization.

21239915 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4247988.

The product of its digits is 4860, while the sum is 32.

The square root of 21239915 is about 4608.6782269974. The cubic root of 21239915 is about 276.9390882935.

The spelling of 21239915 in words is "twenty-one million, two hundred thirty-nine thousand, nine hundred fifteen".