21984991 has 4 divisors (see below), whose sum is σ = 25125712. Its totient is φ = 18844272.

The previous prime is 21984967. The next prime is 21985009. The reversal of 21984991 is 19948912.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21984991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21984091) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1570350 + ... + 1570363.

It is an arithmetic number, because the mean of its divisors is an integer number (6281428).

Almost surely, 2^21984991 is an apocalyptic number.

21984991 is a deficient number, since it is larger than the sum of its proper divisors (3140721).

21984991 is an equidigital number, since it uses as much as digits as its factorization.

21984991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3140720.

The product of its digits is 46656, while the sum is 43.

The square root of 21984991 is about 4688.8155220695. The cubic root of 21984991 is about 280.1401976476.

The spelling of 21984991 in words is "twenty-one million, nine hundred eighty-four thousand, nine hundred ninety-one".