19721001 has 4 divisors (see below), whose sum is σ = 26294672. Its totient is φ = 13147332.

The previous prime is 19720997. The next prime is 19721021. The reversal of 19721001 is 10012791.

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 not a de Polignac number, because 19721001 - 2² = 19720997 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19721021) 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, 3286831 + ... + 3286836.

It is an arithmetic number, because the mean of its divisors is an integer number (6573668).

Almost surely, 2^19721001 is an apocalyptic number.

It is an amenable number.

19721001 is a deficient number, since it is larger than the sum of its proper divisors (6573671).

19721001 is an equidigital number, since it uses as much as digits as its factorization.

19721001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6573670.

The product of its (nonzero) digits is 126, while the sum is 21.

The square root of 19721001 is about 4440.8333677363. The cubic root of 19721001 is about 270.1736468708.

Adding to 19721001 its reverse (10012791), we get a palindrome (29733792).

The spelling of 19721001 in words is "nineteen million, seven hundred twenty-one thousand, one".