21541891 has 4 divisors (see below), whose sum is σ = 24619312. Its totient is φ = 18464472.

The previous prime is 21541889. The next prime is 21541901. The reversal of 21541891 is 19814512.

It is a happy number.

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 21541891 - 2¹ = 21541889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21541841) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1538700 + ... + 1538713.

It is an arithmetic number, because the mean of its divisors is an integer number (6154828).

Almost surely, 2^21541891 is an apocalyptic number.

21541891 is a deficient number, since it is larger than the sum of its proper divisors (3077421).

21541891 is an equidigital number, since it uses as much as digits as its factorization.

21541891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3077420.

The product of its digits is 2880, while the sum is 31.

The square root of 21541891 is about 4641.3242722309. The cubic root of 21541891 is about 278.2453667615.

The spelling of 21541891 in words is "twenty-one million, five hundred forty-one thousand, eight hundred ninety-one".