19899721 has 2 divisors, whose sum is σ = 19899722. Its totient is φ = 19899720.

The previous prime is 19899689. The next prime is 19899731. The reversal of 19899721 is 12799891.

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., 19316025 + 583696 = 4395^2 + 764^2 .

It is a cyclic number.

It is not a de Polignac number, because 19899721 - 2⁵ = 19899689 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (19899731) 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 as a sum of consecutive naturals, namely, 9949860 + 9949861.

It is an arithmetic number, because the mean of its divisors is an integer number (9949861).

Almost surely, 2^19899721 is an apocalyptic number.

It is an amenable number.

19899721 is a deficient number, since it is larger than the sum of its proper divisors (1).

19899721 is an equidigital number, since it uses as much as digits as its factorization.

19899721 is an odious number, because the sum of its binary digits is odd.

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

The square root of 19899721 is about 4460.9103331047. The cubic root of 19899721 is about 270.9873361820.

The spelling of 19899721 in words is "nineteen million, eight hundred ninety-nine thousand, seven hundred twenty-one".