19680721 has 2 divisors, whose sum is σ = 19680722. Its totient is φ = 19680720.

The previous prime is 19680719. The next prime is 19680743. The reversal of 19680721 is 12708691.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12173121 + 7507600 = 3489^2 + 2740^2 .

It is an emirp because it is prime and its reverse (12708691) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19680721 - 2¹ = 19680719 is a prime.

Together with 19680719, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (19680121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9840360 + 9840361.

It is an arithmetic number, because the mean of its divisors is an integer number (9840361).

Almost surely, 2^19680721 is an apocalyptic number.

It is an amenable number.

19680721 is a deficient number, since it is larger than the sum of its proper divisors (1).

19680721 is an equidigital number, since it uses as much as digits as its factorization.

19680721 is an evil number, because the sum of its binary digits is even.

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

The square root of 19680721 is about 4436.2958647953. The cubic root of 19680721 is about 269.9895789302.

The spelling of 19680721 in words is "nineteen million, six hundred eighty thousand, seven hundred twenty-one".