16639421 has 4 divisors (see below), whose sum is σ = 17515200. Its totient is φ = 15763644.

The previous prime is 16639411. The next prime is 16639423. The reversal of 16639421 is 12493661.

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: 12493661 = 2857 ⋅4373.

It is a cyclic number.

It is not a de Polignac number, because 16639421 - 2²² = 12445117 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 (16639423) 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, 437861 + ... + 437898.

It is an arithmetic number, because the mean of its divisors is an integer number (4378800).

Almost surely, 2^16639421 is an apocalyptic number.

It is an amenable number.

16639421 is a deficient number, since it is larger than the sum of its proper divisors (875779).

16639421 is an equidigital number, since it uses as much as digits as its factorization.

16639421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 875778.

The product of its digits is 7776, while the sum is 32.

The square root of 16639421 is about 4079.1446407305. The cubic root of 16639421 is about 255.2972108063.

Subtracting from 16639421 its reverse (12493661), we obtain a triangular number (4145760 = T₂₈₇₉).

The spelling of 16639421 in words is "sixteen million, six hundred thirty-nine thousand, four hundred twenty-one".