21025391 has 4 divisors (see below), whose sum is σ = 21164784. Its totient is φ = 20886000.

The previous prime is 21025363. The next prime is 21025397. The reversal of 21025391 is 19352012.

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 21025391 - 2¹⁸ = 20763247 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 (21025397) 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, 69470 + ... + 69771.

It is an arithmetic number, because the mean of its divisors is an integer number (5291196).

Almost surely, 2^21025391 is an apocalyptic number.

21025391 is a deficient number, since it is larger than the sum of its proper divisors (139393).

21025391 is a wasteful number, since it uses less digits than its factorization.

21025391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 139392.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 21025391 is about 4585.3452432723. The cubic root of 21025391 is about 276.0035662565.

The spelling of 21025391 in words is "twenty-one million, twenty-five thousand, three hundred ninety-one".