21047437 has 4 divisors (see below), whose sum is σ = 21186976. Its totient is φ = 20907900.

The previous prime is 21047431. The next prime is 21047441. The reversal of 21047437 is 73474012.

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 21047437 - 2¹⁹ = 20523149 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 (21047431) 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, 69543 + ... + 69844.

It is an arithmetic number, because the mean of its divisors is an integer number (5296744).

Almost surely, 2^21047437 is an apocalyptic number.

It is an amenable number.

21047437 is a deficient number, since it is larger than the sum of its proper divisors (139539).

21047437 is a wasteful number, since it uses less digits than its factorization.

21047437 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139538.

The product of its (nonzero) digits is 4704, while the sum is 28.

The square root of 21047437 is about 4587.7485763716. The cubic root of 21047437 is about 276.0999996458.

The spelling of 21047437 in words is "twenty-one million, forty-seven thousand, four hundred thirty-seven".