840556021 has 4 divisors (see below), whose sum is σ = 841927852. Its totient is φ = 839184192.

The previous prime is 840556001. The next prime is 840556033. The reversal of 840556021 is 120655048.

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 117483921 + 723072100 = 10839^2 + 26890^2 .

It is a cyclic number.

It is not a de Polignac number, because 840556021 - 2¹⁵ = 840523253 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 (840556001) 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, 684996 + ... + 686221.

It is an arithmetic number, because the mean of its divisors is an integer number (210481963).

Almost surely, 2^840556021 is an apocalyptic number.

It is an amenable number.

840556021 is a deficient number, since it is larger than the sum of its proper divisors (1371831).

840556021 is a wasteful number, since it uses less digits than its factorization.

840556021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1371830.

The product of its (nonzero) digits is 9600, while the sum is 31.

The square root of 840556021 is about 28992.3441791105. The cubic root of 840556021 is about 943.7469356157.

The spelling of 840556021 in words is "eight hundred forty million, five hundred fifty-six thousand, twenty-one".