21821237 has 2 divisors, whose sum is σ = 21821238. Its totient is φ = 21821236.

The previous prime is 21821221. The next prime is 21821243. The reversal of 21821237 is 73212812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19483396 + 2337841 = 4414^2 + 1529^2 .

It is a cyclic number.

It is not a de Polignac number, because 21821237 - 2⁴ = 21821221 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21821257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10910618 + 10910619.

It is an arithmetic number, because the mean of its divisors is an integer number (10910619).

Almost surely, 2^21821237 is an apocalyptic number.

It is an amenable number.

21821237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21821237 is an equidigital number, since it uses as much as digits as its factorization.

21821237 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1344, while the sum is 26.

The square root of 21821237 is about 4671.3206911964. The cubic root of 21821237 is about 279.4429272775.

The spelling of 21821237 in words is "twenty-one million, eight hundred twenty-one thousand, two hundred thirty-seven".