21158921 has 8 divisors (see below), whose sum is σ = 24225984. Its totient is φ = 18102960.

The previous prime is 21158903. The next prime is 21158933. The reversal of 21158921 is 12985112.

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 21158921 - 2¹⁰ = 21157897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21152921) 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, 1826 + ... + 6756.

It is an arithmetic number, because the mean of its divisors is an integer number (3028248).

Almost surely, 2^21158921 is an apocalyptic number.

It is an amenable number.

21158921 is a deficient number, since it is larger than the sum of its proper divisors (3067063).

21158921 is an equidigital number, since it uses as much as digits as its factorization.

21158921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5551.

The product of its digits is 1440, while the sum is 29.

The square root of 21158921 is about 4599.8827158961. The cubic root of 21158921 is about 276.5866233503.

The spelling of 21158921 in words is "twenty-one million, one hundred fifty-eight thousand, nine hundred twenty-one".