21813491 has 8 divisors (see below), whose sum is σ = 25734144. Its totient is φ = 18093960.

The previous prime is 21813487. The next prime is 21813497. The reversal of 21813491 is 19431812.

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 21813491 - 2² = 21813487 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21813497) 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, 50045 + ... + 50478.

It is an arithmetic number, because the mean of its divisors is an integer number (3216768).

Almost surely, 2^21813491 is an apocalyptic number.

21813491 is a deficient number, since it is larger than the sum of its proper divisors (3920653).

21813491 is a wasteful number, since it uses less digits than its factorization.

21813491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 100561.

The product of its digits is 1728, while the sum is 29.

The square root of 21813491 is about 4670.4915158899. The cubic root of 21813491 is about 279.4098582526.

The spelling of 21813491 in words is "twenty-one million, eight hundred thirteen thousand, four hundred ninety-one".