16537991 has 4 divisors (see below), whose sum is σ = 17510832. Its totient is φ = 15565152.

The previous prime is 16537987. The next prime is 16538003. The reversal of 16537991 is 19973561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19973561 = 97 ⋅205913.

It is a cyclic number.

It is not a de Polignac number, because 16537991 - 2² = 16537987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16537951) 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, 486395 + ... + 486428.

It is an arithmetic number, because the mean of its divisors is an integer number (4377708).

Almost surely, 2^16537991 is an apocalyptic number.

16537991 is a deficient number, since it is larger than the sum of its proper divisors (972841).

16537991 is an equidigital number, since it uses as much as digits as its factorization.

16537991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 972840.

The product of its digits is 51030, while the sum is 41.

The square root of 16537991 is about 4066.6928824292. The cubic root of 16537991 is about 254.7774092418. Note that the first 3 decimals are identical.

The spelling of 16537991 in words is "sixteen million, five hundred thirty-seven thousand, nine hundred ninety-one".