21109891 has 8 divisors (see below), whose sum is σ = 23373504. Its totient is φ = 18903720.

The previous prime is 21109889. The next prime is 21109897. The reversal of 21109891 is 19890112.

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

It is not a de Polignac number, because 21109891 - 2¹ = 21109889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21109897) 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, 13585 + ... + 15058.

It is an arithmetic number, because the mean of its divisors is an integer number (2921688).

Almost surely, 2^21109891 is an apocalyptic number.

21109891 is a deficient number, since it is larger than the sum of its proper divisors (2263613).

21109891 is a wasteful number, since it uses less digits than its factorization.

21109891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28721.

The product of its (nonzero) digits is 1296, while the sum is 31.

The square root of 21109891 is about 4594.5501411999. The cubic root of 21109891 is about 276.3728202250.

The spelling of 21109891 in words is "twenty-one million, one hundred nine thousand, eight hundred ninety-one".