19991723 has 4 divisors (see below), whose sum is σ = 20479368. Its totient is φ = 19504080.

The previous prime is 19991717. The next prime is 19991731. The reversal of 19991723 is 32719991.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 19991723 - 2⁸ = 19991467 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (41), and also a Moran number because the ratio is a prime number: 487603 = 19991723 / (1 + 9 + 9 + 9 + 1 + 7 + 2 + 3).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (19991753) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 243761 + ... + 243842.

It is an arithmetic number, because the mean of its divisors is an integer number (5119842).

Almost surely, 2^19991723 is an apocalyptic number.

19991723 is a deficient number, since it is larger than the sum of its proper divisors (487645).

19991723 is an equidigital number, since it uses as much as digits as its factorization.

19991723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 487644.

The product of its digits is 30618, while the sum is 41.

The square root of 19991723 is about 4471.2104625034. The cubic root of 19991723 is about 271.4043111017.

The spelling of 19991723 in words is "nineteen million, nine hundred ninety-one thousand, seven hundred twenty-three".