21899981 has 8 divisors (see below), whose sum is σ = 22842624. Its totient is φ = 20972160.

The previous prime is 21899939. The next prime is 21899987. The reversal of 21899981 is 18999812.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21899981 is a prime.

It is a super-2 number, since 2×21899981² = 959218335600722, 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 (21899987) 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, 635 + ... + 6648.

It is an arithmetic number, because the mean of its divisors is an integer number (2855328).

Almost surely, 2^21899981 is an apocalyptic number.

It is an amenable number.

21899981 is a deficient number, since it is larger than the sum of its proper divisors (942643).

21899981 is an equidigital number, since it uses as much as digits as its factorization.

21899981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7411.

The product of its digits is 93312, while the sum is 47.

The square root of 21899981 is about 4679.7415526928. The cubic root of 21899981 is about 279.7786558526.

The spelling of 21899981 in words is "twenty-one million, eight hundred ninety-nine thousand, nine hundred eighty-one".