21021591 has 8 divisors (see below), whose sum is σ = 28413040. Its totient is φ = 13822272.

The previous prime is 21021577. The next prime is 21021601. The reversal of 21021591 is 19512012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21021591 - 2⁷ = 21021463 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 (21020591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 47776 + ... + 48213.

It is an arithmetic number, because the mean of its divisors is an integer number (3551630).

Almost surely, 2^21021591 is an apocalyptic number.

21021591 is a deficient number, since it is larger than the sum of its proper divisors (7391449).

21021591 is an equidigital number, since it uses as much as digits as its factorization.

21021591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96065.

The product of its (nonzero) digits is 180, while the sum is 21.

The square root of 21021591 is about 4584.9308609836. The cubic root of 21021591 is about 275.9869375250.

It can be divided in two parts, 21021 and 591, that added together give a palindrome (21612).

The spelling of 21021591 in words is "twenty-one million, twenty-one thousand, five hundred ninety-one".