16691981 has 8 divisors (see below), whose sum is σ = 17282304. Its totient is φ = 16104960.

The previous prime is 16691963. The next prime is 16692019. The reversal of 16691981 is 18919661.

It is a happy number.

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 16691981 - 2²² = 12497677 is a prime.

It is a super-2 number, since 2×16691981² = 557244459408722, 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 (16691281) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13901 + ... + 15053.

It is an arithmetic number, because the mean of its divisors is an integer number (2160288).

Almost surely, 2^16691981 is an apocalyptic number.

It is an amenable number.

16691981 is a deficient number, since it is larger than the sum of its proper divisors (590323).

16691981 is a wasteful number, since it uses less digits than its factorization.

16691981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1651.

The product of its digits is 23328, while the sum is 41.

The square root of 16691981 is about 4085.5820882709. The cubic root of 16691981 is about 255.5657361274.

The spelling of 16691981 in words is "sixteen million, six hundred ninety-one thousand, nine hundred eighty-one".