16331981 has 4 divisors (see below), whose sum is σ = 16730364. Its totient is φ = 15933600.

The previous prime is 16331977. The next prime is 16331999. The reversal of 16331981 is 18913361.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3118756 + 13213225 = 1766^2 + 3635^2 .

It is a cyclic number.

It is not a de Polignac number, because 16331981 - 2² = 16331977 is a prime.

It is a super-2 number, since 2×16331981² = 533467206768722, 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 (16331921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 199130 + ... + 199211.

It is an arithmetic number, because the mean of its divisors is an integer number (4182591).

Almost surely, 2^16331981 is an apocalyptic number.

It is an amenable number.

16331981 is a deficient number, since it is larger than the sum of its proper divisors (398383).

16331981 is an equidigital number, since it uses as much as digits as its factorization.

16331981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398382.

The product of its digits is 3888, while the sum is 32.

The square root of 16331981 is about 4041.2845730040. The cubic root of 16331981 is about 253.7150844563.

The spelling of 16331981 in words is "sixteen million, three hundred thirty-one thousand, nine hundred eighty-one".