19992821 has 4 divisors (see below), whose sum is σ = 20138892. Its totient is φ = 19846752.

The previous prime is 19992809. The next prime is 19992829. The reversal of 19992821 is 12829991.

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

It can be written as a sum of positive squares in 2 ways, for example, as 17556100 + 2436721 = 4190^2 + 1561^2 .

It is a cyclic number.

It is not a de Polignac number, because 19992821 - 2⁶ = 19992757 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19992829) 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, 72830 + ... + 73103.

It is an arithmetic number, because the mean of its divisors is an integer number (5034723).

Almost surely, 2^19992821 is an apocalyptic number.

It is an amenable number.

19992821 is a deficient number, since it is larger than the sum of its proper divisors (146071).

19992821 is a wasteful number, since it uses less digits than its factorization.

19992821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 146070.

The product of its digits is 23328, while the sum is 41.

The square root of 19992821 is about 4471.3332463595. Note that the first 3 decimals coincide. The cubic root of 19992821 is about 271.4092797659.

The spelling of 19992821 in words is "nineteen million, nine hundred ninety-two thousand, eight hundred twenty-one".