19721009 has 8 divisors (see below), whose sum is σ = 24587328. Its totient is φ = 15366960.

The previous prime is 19720997. The next prime is 19721021. The reversal of 19721009 is 90012791.

It is an interprime number because it is at equal distance from previous prime (19720997) and next prime (19721021).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-19721009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19721029) 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 7 ways as a sum of consecutive naturals, for example, 127982 + ... + 128135.

It is an arithmetic number, because the mean of its divisors is an integer number (3073416).

Almost surely, 2^19721009 is an apocalyptic number.

It is an amenable number.

19721009 is a deficient number, since it is larger than the sum of its proper divisors (4866319).

19721009 is a wasteful number, since it uses less digits than its factorization.

19721009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 256135.

The product of its (nonzero) digits is 1134, while the sum is 29.

The square root of 19721009 is about 4440.8342684680. The cubic root of 19721009 is about 270.1736834036.

The spelling of 19721009 in words is "nineteen million, seven hundred twenty-one thousand, nine".