19720661 has 2 divisors, whose sum is σ = 19720662. Its totient is φ = 19720660.

The previous prime is 19720639. The next prime is 19720669. The reversal of 19720661 is 16602791.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16851025 + 2869636 = 4105^2 + 1694^2 .

It is an emirp because it is prime and its reverse (16602791) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19720661 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (19720669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9860330 + 9860331.

It is an arithmetic number, because the mean of its divisors is an integer number (9860331).

Almost surely, 2^19720661 is an apocalyptic number.

It is an amenable number.

19720661 is a deficient number, since it is larger than the sum of its proper divisors (1).

19720661 is an equidigital number, since it uses as much as digits as its factorization.

19720661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4536, while the sum is 32.

The square root of 19720661 is about 4440.7950864682. The cubic root of 19720661 is about 270.1720942186.

The spelling of 19720661 in words is "nineteen million, seven hundred twenty thousand, six hundred sixty-one".