21390172 has 12 divisors (see below), whose sum is σ = 37562616. Its totient is φ = 10658000.

The previous prime is 21390163. The next prime is 21390247. The reversal of 21390172 is 27109312.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7954 + ... + 10297.

It is an arithmetic number, because the mean of its divisors is an integer number (3130218).

Almost surely, 2^21390172 is an apocalyptic number.

It is an amenable number.

21390172 is a deficient number, since it is larger than the sum of its proper divisors (16172444).

21390172 is a wasteful number, since it uses less digits than its factorization.

21390172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18548 (or 18546 counting only the distinct ones).

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21390172 is about 4624.9510267677. The cubic root of 21390172 is about 277.5906021285.

Adding to 21390172 its reverse (27109312), we get a palindrome (48499484).

The spelling of 21390172 in words is "twenty-one million, three hundred ninety thousand, one hundred seventy-two".