19639721 has 2 divisors, whose sum is σ = 19639722. Its totient is φ = 19639720.

The previous prime is 19639717. The next prime is 19639747. The reversal of 19639721 is 12793691.

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., 11316496 + 8323225 = 3364^2 + 2885^2 .

It is an emirp because it is prime and its reverse (12793691) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 19639721 - 2² = 19639717 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (19639751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9819860 + 9819861.

It is an arithmetic number, because the mean of its divisors is an integer number (9819861).

Almost surely, 2^19639721 is an apocalyptic number.

It is an amenable number.

19639721 is a deficient number, since it is larger than the sum of its proper divisors (1).

19639721 is an equidigital number, since it uses as much as digits as its factorization.

19639721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20412, while the sum is 38.

The square root of 19639721 is about 4431.6724833859. The cubic root of 19639721 is about 269.8019626912.

The spelling of 19639721 in words is "nineteen million, six hundred thirty-nine thousand, seven hundred twenty-one".