21813539 has 32 divisors (see below), whose sum is σ = 26784000. Its totient is φ = 17539200.

The previous prime is 21813527. The next prime is 21813563. The reversal of 21813539 is 93531812.

It is not a de Polignac number, because 21813539 - 2¹² = 21809443 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21813569) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 357569 + ... + 357629.

It is an arithmetic number, because the mean of its divisors is an integer number (837000).

Almost surely, 2^21813539 is an apocalyptic number.

21813539 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

21813539 is a deficient number, since it is larger than the sum of its proper divisors (4970461).

21813539 is a wasteful number, since it uses less digits than its factorization.

21813539 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179.

The product of its digits is 6480, while the sum is 32.

The square root of 21813539 is about 4670.4966545326. The cubic root of 21813539 is about 279.4100631971.

The spelling of 21813539 in words is "twenty-one million, eight hundred thirteen thousand, five hundred thirty-nine".