21521843 has 24 divisors (see below), whose sum is σ = 26465280. Its totient is φ = 17121600.

The previous prime is 21521839. The next prime is 21521849. The reversal of 21521843 is 34812512.

It is not a de Polignac number, because 21521843 - 2² = 21521839 is a prime.

It is a super-2 number, since 2×21521843² = 926379452233298, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521849) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 364748 + ... + 364806.

It is an arithmetic number, because the mean of its divisors is an integer number (1102720).

Almost surely, 2^21521843 is an apocalyptic number.

21521843 is a deficient number, since it is larger than the sum of its proper divisors (4943437).

21521843 is an equidigital number, since it uses as much as digits as its factorization.

21521843 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 179 (or 138 counting only the distinct ones).

The product of its digits is 1920, while the sum is 26.

The square root of 21521843 is about 4639.1640410746. The cubic root of 21521843 is about 278.1590234520.

The spelling of 21521843 in words is "twenty-one million, five hundred twenty-one thousand, eight hundred forty-three".