21990931 has 4 divisors (see below), whose sum is σ = 22502392. Its totient is φ = 21479472.

The previous prime is 21990907. The next prime is 21990949. The reversal of 21990931 is 13909912.

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 21990931 - 2¹³ = 21982739 is a prime.

It is a super-2 number, since 2×21990931² = 967202092493522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21990131) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 255666 + ... + 255751.

It is an arithmetic number, because the mean of its divisors is an integer number (5625598).

Almost surely, 2^21990931 is an apocalyptic number.

21990931 is a deficient number, since it is larger than the sum of its proper divisors (511461).

21990931 is an equidigital number, since it uses as much as digits as its factorization.

21990931 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 511460.

The product of its (nonzero) digits is 4374, while the sum is 34.

The square root of 21990931 is about 4689.4489015235. The cubic root of 21990931 is about 280.1654252060.

The spelling of 21990931 in words is "twenty-one million, nine hundred ninety thousand, nine hundred thirty-one".