21837391 has 2 divisors, whose sum is σ = 21837392. Its totient is φ = 21837390.

The previous prime is 21837359. The next prime is 21837397. The reversal of 21837391 is 19373812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21837391 - 2⁵ = 21837359 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21837397) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10918695 + 10918696.

It is an arithmetic number, because the mean of its divisors is an integer number (10918696).

Almost surely, 2^21837391 is an apocalyptic number.

21837391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21837391 is an equidigital number, since it uses as much as digits as its factorization.

21837391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 9072, while the sum is 34.

The square root of 21837391 is about 4673.0494326510. The cubic root of 21837391 is about 279.5118663510.

The spelling of 21837391 in words is "twenty-one million, eight hundred thirty-seven thousand, three hundred ninety-one".