1820191921 has 4 divisors (see below), whose sum is σ = 1927262052. Its totient is φ = 1713121792.

The previous prime is 1820191913. The next prime is 1820191937. The reversal of 1820191921 is 1291910281.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1291910281 = 67 ⋅19282243.

It can be written as a sum of positive squares in 2 ways, for example, as 710968896 + 1109223025 = 26664^2 + 33305^2 .

It is a cyclic number.

It is not a de Polignac number, because 1820191921 - 2³ = 1820191913 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1820131921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 53535040 + ... + 53535073.

It is an arithmetic number, because the mean of its divisors is an integer number (481815513).

Almost surely, 2^1820191921 is an apocalyptic number.

It is an amenable number.

1820191921 is a deficient number, since it is larger than the sum of its proper divisors (107070131).

1820191921 is a wasteful number, since it uses less digits than its factorization.

1820191921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107070130.

The product of its (nonzero) digits is 2592, while the sum is 34.

The square root of 1820191921 is about 42663.7073049214. The cubic root of 1820191921 is about 1220.9720643452.

The spelling of 1820191921 in words is "one billion, eight hundred twenty million, one hundred ninety-one thousand, nine hundred twenty-one".