21312491 has 8 divisors (see below), whose sum is σ = 21654864. Its totient is φ = 20972320.

The previous prime is 21312463. The next prime is 21312493. The reversal of 21312491 is 19421312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21312491 - 2⁶ = 21312427 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21312493) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 37985 + ... + 38541.

It is an arithmetic number, because the mean of its divisors is an integer number (2706858).

Almost surely, 2^21312491 is an apocalyptic number.

21312491 is a deficient number, since it is larger than the sum of its proper divisors (342373).

21312491 is an equidigital number, since it uses as much as digits as its factorization.

21312491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1101.

The product of its digits is 432, while the sum is 23.

The square root of 21312491 is about 4616.5453534001. The cubic root of 21312491 is about 277.2541598929.

The spelling of 21312491 in words is "twenty-one million, three hundred twelve thousand, four hundred ninety-one".