21011891 has 8 divisors (see below), whose sum is σ = 22188480. Its totient is φ = 19842408.

The previous prime is 21011873. The next prime is 21011917. The reversal of 21011891 is 19811012.

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

It is a cyclic number.

It is not a de Polignac number, because 21011891 - 2¹⁸ = 20749747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21011191) 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, 5000 + ... + 8186.

It is an arithmetic number, because the mean of its divisors is an integer number (2773560).

Almost surely, 2^21011891 is an apocalyptic number.

21011891 is a deficient number, since it is larger than the sum of its proper divisors (1176589).

21011891 is a wasteful number, since it uses less digits than its factorization.

21011891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3553.

The product of its (nonzero) digits is 144, while the sum is 23.

The square root of 21011891 is about 4583.8729258128. The cubic root of 21011891 is about 275.9444814115.

The spelling of 21011891 in words is "twenty-one million, eleven thousand, eight hundred ninety-one".