21624991 has 6 divisors (see below), whose sum is σ = 22606640. Its totient is φ = 20684268.

The previous prime is 21624973. The next prime is 21625027. The reversal of 21624991 is 19942612.

It is not a de Polignac number, because 21624991 - 2⁹ = 21624479 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 (21624971) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 19911 + ... + 20968.

Almost surely, 2^21624991 is an apocalyptic number.

21624991 is a deficient number, since it is larger than the sum of its proper divisors (981649).

21624991 is an equidigital number, since it uses as much as digits as its factorization.

21624991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40925 (or 40902 counting only the distinct ones).

The product of its digits is 7776, while the sum is 34.

The square root of 21624991 is about 4650.2678417485. The cubic root of 21624991 is about 278.6026941270.

The spelling of 21624991 in words is "twenty-one million, six hundred twenty-four thousand, nine hundred ninety-one".