21730237 has 4 divisors (see below), whose sum is σ = 21766300. Its totient is φ = 21694176.

The previous prime is 21730169. The next prime is 21730249. The reversal of 21730237 is 73203712.

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 2493241 + 19236996 = 1579^2 + 4386^2 .

It is a cyclic number.

It is not a de Polignac number, because 21730237 - 2⁷ = 21730109 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 (21730277) 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, 17112 + ... + 18337.

It is an arithmetic number, because the mean of its divisors is an integer number (5441575).

Almost surely, 2^21730237 is an apocalyptic number.

It is an amenable number.

21730237 is a deficient number, since it is larger than the sum of its proper divisors (36063).

21730237 is an equidigital number, since it uses as much as digits as its factorization.

21730237 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36062.

The product of its (nonzero) digits is 1764, while the sum is 25.

The square root of 21730237 is about 4661.5702290108. The cubic root of 21730237 is about 279.0539371489.

Adding to 21730237 its reverse (73203712), we get a palindrome (94933949).

The spelling of 21730237 in words is "twenty-one million, seven hundred thirty thousand, two hundred thirty-seven".