21133621 has 4 divisors (see below), whose sum is σ = 21143232. Its totient is φ = 21124012.

The previous prime is 21133603. The next prime is 21133631. The reversal of 21133621 is 12633112.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21133621 - 2⁵ = 21133589 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 (21133631) 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, 306 + ... + 6508.

It is an arithmetic number, because the mean of its divisors is an integer number (5285808).

Almost surely, 2^21133621 is an apocalyptic number.

It is an amenable number.

21133621 is a deficient number, since it is larger than the sum of its proper divisors (9611).

21133621 is an equidigital number, since it uses as much as digits as its factorization.

21133621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9610.

The product of its digits is 216, while the sum is 19.

The square root of 21133621 is about 4597.1318232133. The cubic root of 21133621 is about 276.4763399624.

Adding to 21133621 its reverse (12633112), we get a palindrome (33766733).

The spelling of 21133621 in words is "twenty-one million, one hundred thirty-three thousand, six hundred twenty-one".