21991837 has 12 divisors (see below), whose sum is σ = 26019360. Its totient is φ = 18528216.

The previous prime is 21991813. The next prime is 21991843. The reversal of 21991837 is 73819912.

It is not a de Polignac number, because 21991837 - 2²³ = 13603229 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21991837.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991807) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 913 + ... + 6694.

It is an arithmetic number, because the mean of its divisors is an integer number (2168280).

Almost surely, 2^21991837 is an apocalyptic number.

It is an amenable number.

21991837 is a deficient number, since it is larger than the sum of its proper divisors (4027523).

21991837 is an equidigital number, since it uses as much as digits as its factorization.

21991837 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7680 (or 7673 counting only the distinct ones).

The product of its digits is 27216, while the sum is 40.

The square root of 21991837 is about 4689.5455003657. The cubic root of 21991837 is about 280.1692726464.

The spelling of 21991837 in words is "twenty-one million, nine hundred ninety-one thousand, eight hundred thirty-seven".