21800991 has 8 divisors (see below), whose sum is σ = 29163904. Its totient is φ = 14486040.

The previous prime is 21800963. The next prime is 21801001. The reversal of 21800991 is 19900812.

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

It is not a de Polignac number, because 21800991 - 2¹⁵ = 21768223 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 (21800921) 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, 10915 + ... + 12756.

It is an arithmetic number, because the mean of its divisors is an integer number (3645488).

Almost surely, 2^21800991 is an apocalyptic number.

21800991 is a deficient number, since it is larger than the sum of its proper divisors (7362913).

21800991 is a wasteful number, since it uses less digits than its factorization.

21800991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23981.

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 21800991 is about 4669.1531352056. The cubic root of 21800991 is about 279.3564770587.

It can be divided in two parts, 21800 and 991, that added together give a triangular number (22791 = T₂₁₃).

The spelling of 21800991 in words is "twenty-one million, eight hundred thousand, nine hundred ninety-one".