21166981 has 8 divisors (see below), whose sum is σ = 23527584. Its totient is φ = 18879120.

The previous prime is 21166973. The next prime is 21166987. The reversal of 21166981 is 18966112.

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

It is a cyclic number.

It is not a de Polignac number, because 21166981 - 2³ = 21166973 is a prime.

It is a super-2 number, since 2×21166981² = 896082169308722, 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 (21166987) 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, 17571 + ... + 18736.

It is an arithmetic number, because the mean of its divisors is an integer number (2940948).

Almost surely, 2^21166981 is an apocalyptic number.

It is an amenable number.

21166981 is a deficient number, since it is larger than the sum of its proper divisors (2360603).

21166981 is a wasteful number, since it uses less digits than its factorization.

21166981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36371.

The product of its digits is 5184, while the sum is 34.

The square root of 21166981 is about 4600.7587417729. The cubic root of 21166981 is about 276.6217386441.

The spelling of 21166981 in words is "twenty-one million, one hundred sixty-six thousand, nine hundred eighty-one".