21991238 has 4 divisors (see below), whose sum is σ = 32986860. Its totient is φ = 10995618.

The previous prime is 21991231. The next prime is 21991267. The reversal of 21991238 is 83219912.

It is a semiprime because it is the product of two primes.

It is a super-2 number, since 2×21991238² = 967229097545288, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21991198 and 21991207.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5497808 + ... + 5497811.

It is an arithmetic number, because the mean of its divisors is an integer number (8246715).

Almost surely, 2^21991238 is an apocalyptic number.

21991238 is a deficient number, since it is larger than the sum of its proper divisors (10995622).

21991238 is a wasteful number, since it uses less digits than its factorization.

21991238 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10995621.

The product of its digits is 7776, while the sum is 35.

The square root of 21991238 is about 4689.4816344666. The cubic root of 21991238 is about 280.1667289311.

The spelling of 21991238 in words is "twenty-one million, nine hundred ninety-one thousand, two hundred thirty-eight".