21019591 has 4 divisors (see below), whose sum is σ = 21095752. Its totient is φ = 20943432.

The previous prime is 21019571. The next prime is 21019597. The reversal of 21019591 is 19591012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21019591 - 2¹⁹ = 20495303 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 (21019597) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 37665 + ... + 38218.

It is an arithmetic number, because the mean of its divisors is an integer number (5273938).

Almost surely, 2^21019591 is an apocalyptic number.

21019591 is a deficient number, since it is larger than the sum of its proper divisors (76161).

21019591 is an equidigital number, since it uses as much as digits as its factorization.

21019591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76160.

The product of its (nonzero) digits is 810, while the sum is 28.

The square root of 21019591 is about 4584.7127499986. The cubic root of 21019591 is about 275.9781847562.

The spelling of 21019591 in words is "twenty-one million, nineteen thousand, five hundred ninety-one".