21865237 has 2 divisors, whose sum is σ = 21865238. Its totient is φ = 21865236.

The previous prime is 21865229. The next prime is 21865243. The reversal of 21865237 is 73256812.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13256881 + 8608356 = 3641^2 + 2934^2 .

It is a cyclic number.

It is not a de Polignac number, because 21865237 - 2³ = 21865229 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21865037) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932618 + 10932619.

It is an arithmetic number, because the mean of its divisors is an integer number (10932619).

Almost surely, 2^21865237 is an apocalyptic number.

It is an amenable number.

21865237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21865237 is an equidigital number, since it uses as much as digits as its factorization.

21865237 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20160, while the sum is 34.

The square root of 21865237 is about 4676.0279083855. The cubic root of 21865237 is about 279.6306226237.

The spelling of 21865237 in words is "twenty-one million, eight hundred sixty-five thousand, two hundred thirty-seven".