21056989 has 4 divisors (see below), whose sum is σ = 21070720. Its totient is φ = 21043260.

The previous prime is 21056963. The next prime is 21056993. The reversal of 21056989 is 98965012.

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 21056989 - 2¹¹ = 21054941 is a prime.

It is a super-2 number, since 2×21056989² = 886793571492242, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21056939) 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, 4227 + ... + 7744.

It is an arithmetic number, because the mean of its divisors is an integer number (5267680).

Almost surely, 2^21056989 is an apocalyptic number.

It is an amenable number.

21056989 is a deficient number, since it is larger than the sum of its proper divisors (13731).

21056989 is a wasteful number, since it uses less digits than its factorization.

21056989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13730.

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 21056989 is about 4588.7894917941. The cubic root of 21056989 is about 276.1417609987.

The spelling of 21056989 in words is "twenty-one million, fifty-six thousand, nine hundred eighty-nine".