19721989 has 24 divisors (see below), whose sum is σ = 24736320. Its totient is φ = 15345408.

The previous prime is 19721963. The next prime is 19722013. The reversal of 19721989 is 98912791.

It is a happy number.

It is not a de Polignac number, because 19721989 - 2¹¹ = 19719941 is a prime.

It is a super-2 number, since 2×19721989² = 777913700232242, which contains 22 as substring.

Its product of digits (81648) is a multiple of the sum of its prime factors (189).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19721909) 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 23 ways as a sum of consecutive naturals, for example, 334242 + ... + 334300.

It is an arithmetic number, because the mean of its divisors is an integer number (1030680).

Almost surely, 2^19721989 is an apocalyptic number.

19721989 is the 2809-th heptagonal number.

It is an amenable number.

19721989 is a deficient number, since it is larger than the sum of its proper divisors (5014331).

19721989 is an equidigital number, since it uses as much as digits as its factorization.

19721989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 189 (or 136 counting only the distinct ones).

The product of its digits is 81648, while the sum is 46.

The square root of 19721989 is about 4440.9446067250. The cubic root of 19721989 is about 270.1781585942.

The spelling of 19721989 in words is "nineteen million, seven hundred twenty-one thousand, nine hundred eighty-nine".