840206021 has 4 divisors (see below), whose sum is σ = 842627712. Its totient is φ = 837784332.

The previous prime is 840205987. The next prime is 840206039. The reversal of 840206021 is 120602048.

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 not a de Polignac number, because 840206021 - 2⁶ = 840205957 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (840206221) 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, 1210325 + ... + 1211018.

It is an arithmetic number, because the mean of its divisors is an integer number (210656928).

Almost surely, 2^840206021 is an apocalyptic number.

It is an amenable number.

840206021 is a deficient number, since it is larger than the sum of its proper divisors (2421691).

840206021 is a wasteful number, since it uses less digits than its factorization.

840206021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2421690.

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 840206021 is about 28986.3074743921. The cubic root of 840206021 is about 943.6159281730.

Adding to 840206021 its reverse (120602048), we get a palindrome (960808069).

The spelling of 840206021 in words is "eight hundred forty million, two hundred six thousand, twenty-one".