840836021 has 4 divisors (see below), whose sum is σ = 841485612. Its totient is φ = 840186432.

The previous prime is 840835999. The next prime is 840836023. The reversal of 840836021 is 120638048.

840836021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 565773796 + 275062225 = 23786^2 + 16585^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-840836021 is a prime.

It is a super-2 number, since 2×840836021² = 1414010428422224882, which contains 22 as substring.

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 (840836023) 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, 322850 + ... + 325443.

It is an arithmetic number, because the mean of its divisors is an integer number (210371403).

Almost surely, 2^840836021 is an apocalyptic number.

It is an amenable number.

840836021 is a deficient number, since it is larger than the sum of its proper divisors (649591).

840836021 is a wasteful number, since it uses less digits than its factorization.

840836021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 649590.

The product of its (nonzero) digits is 9216, while the sum is 32.

The square root of 840836021 is about 28997.1726380349. The cubic root of 840836021 is about 943.8517153881.

The spelling of 840836021 in words is "eight hundred forty million, eight hundred thirty-six thousand, twenty-one".