21939981 has 8 divisors (see below), whose sum is σ = 33432384. Its totient is φ = 12537120.

The previous prime is 21939977. The next prime is 21939997. The reversal of 21939981 is 18993912.

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

It is not a de Polignac number, because 21939981 - 2² = 21939977 is a prime.

It is a super-2 number, since 2×21939981² = 962725532560722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21939481) 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, 522360 + ... + 522401.

It is an arithmetic number, because the mean of its divisors is an integer number (4179048).

Almost surely, 2^21939981 is an apocalyptic number.

21939981 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21939981 is a deficient number, since it is larger than the sum of its proper divisors (11492403).

21939981 is a wasteful number, since it uses less digits than its factorization.

21939981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1044771.

The product of its digits is 34992, while the sum is 42.

The square root of 21939981 is about 4684.0133432773. The cubic root of 21939981 is about 279.9488894805.

The spelling of 21939981 in words is "twenty-one million, nine hundred thirty-nine thousand, nine hundred eighty-one".