19821397 has 4 divisors (see below), whose sum is σ = 19940256. Its totient is φ = 19702540.

The previous prime is 19821383. The next prime is 19821419. The reversal of 19821397 is 79312891.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-19821397 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19821497) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 59179 + ... + 59512.

It is an arithmetic number, because the mean of its divisors is an integer number (4985064).

Almost surely, 2^19821397 is an apocalyptic number.

It is an amenable number.

19821397 is a deficient number, since it is larger than the sum of its proper divisors (118859).

19821397 is a wasteful number, since it uses less digits than its factorization.

19821397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118858.

The product of its digits is 27216, while the sum is 40.

The square root of 19821397 is about 4452.1227521262. The cubic root of 19821397 is about 270.6313392367.

The spelling of 19821397 in words is "nineteen million, eight hundred twenty-one thousand, three hundred ninety-seven".