1820021 has 4 divisors (see below), whose sum is σ = 2080032. Its totient is φ = 1560012.

The previous prime is 1820009. The next prime is 1820023. The reversal of 1820021 is 1200281.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1200281 = 29 ⋅41389.

It is a cyclic number.

It is not a de Polignac number, because 1820021 - 2⁶ = 1819957 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1819978 and 1820005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1820023) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 129995 + ... + 130008.

It is an arithmetic number, because the mean of its divisors is an integer number (520008).

2^1820021 is an apocalyptic number.

It is an amenable number.

1820021 is a deficient number, since it is larger than the sum of its proper divisors (260011).

1820021 is an equidigital number, since it uses as much as digits as its factorization.

1820021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 260010.

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 1820021 is about 1349.0815394186. The cubic root of 1820021 is about 122.0933845610.

The spelling of 1820021 in words is "one million, eight hundred twenty thousand, twenty-one".