19721680 has 80 divisors (see below), whose sum is σ = 50871744. Its totient is φ = 7050240.

The previous prime is 19721659. The next prime is 19721707. The reversal of 19721680 is 8612791.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 64087 + ... + 64393.

Almost surely, 2^19721680 is an apocalyptic number.

19721680 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 19721680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25435872).

19721680 is an abundant number, since it is smaller than the sum of its proper divisors (31150064).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

19721680 is a wasteful number, since it uses less digits than its factorization.

19721680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 404 (or 398 counting only the distinct ones).

The product of its (nonzero) digits is 6048, while the sum is 34.

The square root of 19721680 is about 4440.9098166930. The cubic root of 19721680 is about 270.1767475552.

Subtracting from 19721680 its reverse (8612791), we obtain a square (11108889 = 3333²).

The spelling of 19721680 in words is "nineteen million, seven hundred twenty-one thousand, six hundred eighty".