21047989 has 8 divisors (see below), whose sum is σ = 22652568. Its totient is φ = 19484160.

The previous prime is 21047987. The next prime is 21048007. The reversal of 21047989 is 98974012.

It can be written as a sum of positive squares in 4 ways, for example, as 1067089 + 19980900 = 1033^2 + 4470^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21047989 - 2¹ = 21047987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21047981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9112 + ... + 11185.

It is an arithmetic number, because the mean of its divisors is an integer number (2831571).

Almost surely, 2^21047989 is an apocalyptic number.

It is an amenable number.

21047989 is a deficient number, since it is larger than the sum of its proper divisors (1604579).

21047989 is a wasteful number, since it uses less digits than its factorization.

21047989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20375.

The product of its (nonzero) digits is 36288, while the sum is 40.

The square root of 21047989 is about 4587.8087362051. The cubic root of 21047989 is about 276.1024133343.

The spelling of 21047989 in words is "twenty-one million, forty-seven thousand, nine hundred eighty-nine".