19999821 has 12 divisors (see below), whose sum is σ = 27621152. Its totient is φ = 12871824.

The previous prime is 19999817. The next prime is 19999831. The reversal of 19999821 is 12899991.

It is not a de Polignac number, because 19999821 - 2² = 19999817 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 (19999831) 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 11 ways as a sum of consecutive naturals, for example, 1441 + ... + 6486.

Almost surely, 2^19999821 is an apocalyptic number.

It is an amenable number.

19999821 is a deficient number, since it is larger than the sum of its proper divisors (7621331).

19999821 is an equidigital number, since it uses as much as digits as its factorization.

19999821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7988 (or 7959 counting only the distinct ones).

The product of its digits is 104976, while the sum is 48.

The square root of 19999821 is about 4472.1159421464. The cubic root of 19999821 is about 271.4409518558.

The spelling of 19999821 in words is "nineteen million, nine hundred ninety-nine thousand, eight hundred twenty-one".