21391885 has 4 divisors (see below), whose sum is σ = 25670268. Its totient is φ = 17113504.

The previous prime is 21391871. The next prime is 21391889. The reversal of 21391885 is 58819312.

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

It can be written as a sum of positive squares in 2 ways, for example, as 12517444 + 8874441 = 3538^2 + 2979^2 .

It is a cyclic number.

It is not a de Polignac number, because 21391885 - 2⁷ = 21391757 is a prime.

It is a super-2 number, since 2×21391885² = 915225487706450, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21391889) 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 3 ways as a sum of consecutive naturals, for example, 2139184 + ... + 2139193.

It is an arithmetic number, because the mean of its divisors is an integer number (6417567).

Almost surely, 2^21391885 is an apocalyptic number.

It is an amenable number.

21391885 is a deficient number, since it is larger than the sum of its proper divisors (4278383).

21391885 is an equidigital number, since it uses as much as digits as its factorization.

21391885 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4278382.

The product of its digits is 17280, while the sum is 37.

The square root of 21391885 is about 4625.1362142103. The cubic root of 21391885 is about 277.5980120737.

The spelling of 21391885 in words is "twenty-one million, three hundred ninety-one thousand, eight hundred eighty-five".