21991002 has 16 divisors (see below), whose sum is σ = 47980512. Its totient is φ = 6663920.

The previous prime is 21991001. The next prime is 21991027. The reversal of 21991002 is 20019912.

It is not an unprimeable number, because it can be changed into a prime (21991001) 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, 166533 + ... + 166664.

It is an arithmetic number, because the mean of its divisors is an integer number (2998782).

Almost surely, 2^21991002 is an apocalyptic number.

21991002 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

21991002 is an abundant number, since it is smaller than the sum of its proper divisors (25989510).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21991002 is a wasteful number, since it uses less digits than its factorization.

21991002 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333213.

The product of its (nonzero) digits is 324, while the sum is 24.

The square root of 21991002 is about 4689.4564717033. The cubic root of 21991002 is about 280.1657267201.

The spelling of 21991002 in words is "twenty-one million, nine hundred ninety-one thousand, two".