16991857 has 4 divisors (see below), whose sum is σ = 17991396. Its totient is φ = 15992320.

The previous prime is 16991851. The next prime is 16991861. The reversal of 16991857 is 75819961.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 75819961 = 7 ⋅10831423.

It can be written as a sum of positive squares in 2 ways, for example, as 12895281 + 4096576 = 3591^2 + 2024^2 .

It is a cyclic number.

It is not a de Polignac number, because 16991857 - 2⁷ = 16991729 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16991851) 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, 499744 + ... + 499777.

It is an arithmetic number, because the mean of its divisors is an integer number (4497849).

Almost surely, 2^16991857 is an apocalyptic number.

16991857 is a gapful number since it is divisible by the number (17) formed by its first and last digit.

It is an amenable number.

16991857 is a deficient number, since it is larger than the sum of its proper divisors (999539).

16991857 is an equidigital number, since it uses as much as digits as its factorization.

16991857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 999538.

The product of its digits is 136080, while the sum is 46.

The square root of 16991857 is about 4122.1180235408. The cubic root of 16991857 is about 257.0870977129.

The spelling of 16991857 in words is "sixteen million, nine hundred ninety-one thousand, eight hundred fifty-seven".