21000991 has 8 divisors (see below), whose sum is σ = 23299200. Its totient is φ = 18767640.

The previous prime is 21000983. The next prime is 21001021. The reversal of 21000991 is 19900012.

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 21000991 - 2³ = 21000983 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000911) 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, 15531 + ... + 16828.

It is an arithmetic number, because the mean of its divisors is an integer number (2912400).

Almost surely, 2^21000991 is an apocalyptic number.

21000991 is a deficient number, since it is larger than the sum of its proper divisors (2298209).

21000991 is a wasteful number, since it uses less digits than its factorization.

21000991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32429.

The product of its (nonzero) digits is 162, while the sum is 22.

The square root of 21000991 is about 4582.6838206448. The cubic root of 21000991 is about 275.8967574014.

The spelling of 21000991 in words is "twenty-one million, nine hundred ninety-one", and thus it is an aban number.