21996991 has 4 divisors (see below), whose sum is σ = 22007272. Its totient is φ = 21986712.

The previous prime is 21996983. The next prime is 21997009. The reversal of 21996991 is 19969912.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21996991 - 2³ = 21996983 is a prime.

It is a super-2 number, since 2×21996991² = 967735226108162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21996941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 585 + ... + 6658.

It is an arithmetic number, because the mean of its divisors is an integer number (5501818).

Almost surely, 2^21996991 is an apocalyptic number.

21996991 is a deficient number, since it is larger than the sum of its proper divisors (10281).

21996991 is an equidigital number, since it uses as much as digits as its factorization.

21996991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10280.

The product of its digits is 78732, while the sum is 46.

The square root of 21996991 is about 4690.0949883771. The cubic root of 21996991 is about 280.1911577310.

The spelling of 21996991 in words is "twenty-one million, nine hundred ninety-six thousand, nine hundred ninety-one".