21397237 has 4 divisors (see below), whose sum is σ = 22655916. Its totient is φ = 20138560.

The previous prime is 21397217. The next prime is 21397253. The reversal of 21397237 is 73279312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17859076 + 3538161 = 4226^2 + 1881^2 .

It is a cyclic number.

It is not a de Polignac number, because 21397237 - 2¹⁹ = 20872949 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 (21397217) 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, 629314 + ... + 629347.

It is an arithmetic number, because the mean of its divisors is an integer number (5663979).

Almost surely, 2^21397237 is an apocalyptic number.

It is an amenable number.

21397237 is a deficient number, since it is larger than the sum of its proper divisors (1258679).

21397237 is a wasteful number, since it uses less digits than its factorization.

21397237 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1258678.

The product of its digits is 15876, while the sum is 34.

The square root of 21397237 is about 4625.7147555810. The cubic root of 21397237 is about 277.6211607378.

The spelling of 21397237 in words is "twenty-one million, three hundred ninety-seven thousand, two hundred thirty-seven".