21547891 has 8 divisors (see below), whose sum is σ = 22857120. Its totient is φ = 20243328.

The previous prime is 21547873. The next prime is 21547901. The reversal of 21547891 is 19874512.

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

It is not a de Polignac number, because 21547891 - 2⁷ = 21547763 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 21547891.

It is not an unprimeable number, because it can be changed into a prime (21547811) 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 7 ways as a sum of consecutive naturals, for example, 14365 + ... + 15793.

It is an arithmetic number, because the mean of its divisors is an integer number (2857140).

Almost surely, 2^21547891 is an apocalyptic number.

21547891 is a deficient number, since it is larger than the sum of its proper divisors (1309229).

21547891 is a wasteful number, since it uses less digits than its factorization.

21547891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2333.

The product of its digits is 20160, while the sum is 37.

The square root of 21547891 is about 4641.9705944782. The cubic root of 21547891 is about 278.2711973200.

The spelling of 21547891 in words is "twenty-one million, five hundred forty-seven thousand, eight hundred ninety-one".