21491821 has 8 divisors (see below), whose sum is σ = 24151680. Its totient is φ = 18975792.

The previous prime is 21491819. The next prime is 21491837. The reversal of 21491821 is 12819412.

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 21491821 - 2¹ = 21491819 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21491821.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21491851) 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, 35641 + ... + 36238.

It is an arithmetic number, because the mean of its divisors is an integer number (3018960).

Almost surely, 2^21491821 is an apocalyptic number.

It is an amenable number.

21491821 is a deficient number, since it is larger than the sum of its proper divisors (2659859).

21491821 is a wasteful number, since it uses less digits than its factorization.

21491821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71915.

The product of its digits is 1152, while the sum is 28.

The square root of 21491821 is about 4635.9271996010. The cubic root of 21491821 is about 278.0296235016.

The spelling of 21491821 in words is "twenty-one million, four hundred ninety-one thousand, eight hundred twenty-one".