19639921 has 4 divisors (see below), whose sum is σ = 22445632. Its totient is φ = 16834212.

The previous prime is 19639891. The next prime is 19639927. The reversal of 19639921 is 12993691.

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 19639921 - 2⁵ = 19639889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19639927) 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, 1402845 + ... + 1402858.

It is an arithmetic number, because the mean of its divisors is an integer number (5611408).

Almost surely, 2^19639921 is an apocalyptic number.

It is an amenable number.

19639921 is a deficient number, since it is larger than the sum of its proper divisors (2805711).

19639921 is an equidigital number, since it uses as much as digits as its factorization.

19639921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2805710.

The product of its digits is 26244, while the sum is 40.

The square root of 19639921 is about 4431.6950481729. The cubic root of 19639921 is about 269.8028785258.

The spelling of 19639921 in words is "nineteen million, six hundred thirty-nine thousand, nine hundred twenty-one".