21621893 has 4 divisors (see below), whose sum is σ = 21708288. Its totient is φ = 21535500.

The previous prime is 21621881. The next prime is 21621923. The reversal of 21621893 is 39812612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21621893 - 2¹⁰ = 21620869 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21621823) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 42821 + ... + 43322.

It is an arithmetic number, because the mean of its divisors is an integer number (5427072).

Almost surely, 2^21621893 is an apocalyptic number.

It is an amenable number.

21621893 is a deficient number, since it is larger than the sum of its proper divisors (86395).

21621893 is an equidigital number, since it uses as much as digits as its factorization.

21621893 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86394.

The product of its digits is 5184, while the sum is 32.

The square root of 21621893 is about 4649.9347307247. The cubic root of 21621893 is about 278.5893892681.

The spelling of 21621893 in words is "twenty-one million, six hundred twenty-one thousand, eight hundred ninety-three".