21989257 has 4 divisors (see below), whose sum is σ = 22104576. Its totient is φ = 21873940.

The previous prime is 21989237. The next prime is 21989269. The reversal of 21989257 is 75298912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21989257 - 2⁷ = 21989129 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21989207) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 57373 + ... + 57754.

It is an arithmetic number, because the mean of its divisors is an integer number (5526144).

Almost surely, 2^21989257 is an apocalyptic number.

It is an amenable number.

21989257 is a deficient number, since it is larger than the sum of its proper divisors (115319).

21989257 is a wasteful number, since it uses less digits than its factorization.

21989257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 115318.

The product of its digits is 90720, while the sum is 43.

The square root of 21989257 is about 4689.2704123350. The cubic root of 21989257 is about 280.1583160812.

The spelling of 21989257 in words is "twenty-one million, nine hundred eighty-nine thousand, two hundred fifty-seven".