16581491 has 4 divisors (see below), whose sum is σ = 16781352. Its totient is φ = 16381632.

The previous prime is 16581479. The next prime is 16581493. The reversal of 16581491 is 19418561.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16581491 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16581493) 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, 99806 + ... + 99971.

It is an arithmetic number, because the mean of its divisors is an integer number (4195338).

Almost surely, 2^16581491 is an apocalyptic number.

16581491 is a deficient number, since it is larger than the sum of its proper divisors (199861).

16581491 is an equidigital number, since it uses as much as digits as its factorization.

16581491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 199860.

The product of its digits is 8640, while the sum is 35.

The square root of 16581491 is about 4072.0376962892. The cubic root of 16581491 is about 255.0005946417. Note that the first 3 decimals are identical.

The spelling of 16581491 in words is "sixteen million, five hundred eighty-one thousand, four hundred ninety-one".