21990981 has 8 divisors (see below), whose sum is σ = 29370304. Its totient is φ = 14636160.

The previous prime is 21990977. The next prime is 21990989. The reversal of 21990981 is 18909912.

It is a happy number.

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

It is not a de Polignac number, because 21990981 - 2² = 21990977 is a prime.

It is a super-2 number, since 2×21990981² = 967206490684722, 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 (21990989) 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 7 ways as a sum of consecutive naturals, for example, 3916 + ... + 7701.

It is an arithmetic number, because the mean of its divisors is an integer number (3671288).

Almost surely, 2^21990981 is an apocalyptic number.

It is an amenable number.

21990981 is a deficient number, since it is larger than the sum of its proper divisors (7379323).

21990981 is a wasteful number, since it uses less digits than its factorization.

21990981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12251.

The product of its (nonzero) digits is 11664, while the sum is 39.

The square root of 21990981 is about 4689.4542326373. The cubic root of 21990981 is about 280.1656375399.

The spelling of 21990981 in words is "twenty-one million, nine hundred ninety thousand, nine hundred eighty-one".