21239391 has 16 divisors (see below), whose sum is σ = 28827648. Its totient is φ = 13908000.

The previous prime is 21239381. The next prime is 21239429. The reversal of 21239391 is 19393212.

It is a happy number.

It is not a de Polignac number, because 21239391 - 2¹¹ = 21237343 is a prime.

It is a super-2 number, since 2×21239391² = 902223460101762, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21239381) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 57690 + ... + 58056.

It is an arithmetic number, because the mean of its divisors is an integer number (1801728).

Almost surely, 2^21239391 is an apocalyptic number.

21239391 is a deficient number, since it is larger than the sum of its proper divisors (7588257).

21239391 is a wasteful number, since it uses less digits than its factorization.

21239391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 662.

The product of its digits is 2916, while the sum is 30.

The square root of 21239391 is about 4608.6213773752. The cubic root of 21239391 is about 276.9368108633.

The spelling of 21239391 in words is "twenty-one million, two hundred thirty-nine thousand, three hundred ninety-one".