16621921 has 4 divisors (see below), whose sum is σ = 17158144. Its totient is φ = 16085700.

The previous prime is 16621897. The next prime is 16621949. The reversal of 16621921 is 12912661.

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, and also an emirpimes, since its reverse is a distinct semiprime: 12912661 = 137 ⋅94253.

It is a cyclic number.

It is not a de Polignac number, because 16621921 - 2¹¹ = 16619873 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 16621921.

It is not an unprimeable number, because it can be changed into a prime (16621021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 268065 + ... + 268126.

It is an arithmetic number, because the mean of its divisors is an integer number (4289536).

Almost surely, 2^16621921 is an apocalyptic number.

It is an amenable number.

16621921 is a deficient number, since it is larger than the sum of its proper divisors (536223).

16621921 is an equidigital number, since it uses as much as digits as its factorization.

16621921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 536222.

The product of its digits is 1296, while the sum is 28.

The square root of 16621921 is about 4076.9990188863. Note that the first 3 decimals coincide. The cubic root of 16621921 is about 255.2076790780.

The spelling of 16621921 in words is "sixteen million, six hundred twenty-one thousand, nine hundred twenty-one".