16581921 has 4 divisors (see below), whose sum is σ = 22109232. Its totient is φ = 11054612.

The previous prime is 16581913. The next prime is 16581923. The reversal of 16581921 is 12918561.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 16581921 - 2³ = 16581913 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (16581923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2763651 + ... + 2763656.

It is an arithmetic number, because the mean of its divisors is an integer number (5527308).

Almost surely, 2^16581921 is an apocalyptic number.

It is an amenable number.

16581921 is a deficient number, since it is larger than the sum of its proper divisors (5527311).

16581921 is an equidigital number, since it uses as much as digits as its factorization.

16581921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5527310.

The product of its digits is 4320, while the sum is 33.

The square root of 16581921 is about 4072.0904950652. The cubic root of 16581921 is about 255.0027988928.

It can be divided in two parts, 16581 and 921, that multiplied together give a triangular number (15271101 = T₅₅₂₆).

The spelling of 16581921 in words is "sixteen million, five hundred eighty-one thousand, nine hundred twenty-one".