851021921 has 4 divisors (see below), whose sum is σ = 901082052. Its totient is φ = 800961792.

The previous prime is 851021911. The next prime is 851021923. The reversal of 851021921 is 129120158.

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 679123600 + 171898321 = 26060^2 + 13111^2 .

It is a cyclic number.

It is not a de Polignac number, because 851021921 - 2²⁶ = 783913057 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (851021923) 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, 25030040 + ... + 25030073.

It is an arithmetic number, because the mean of its divisors is an integer number (225270513).

Almost surely, 2^851021921 is an apocalyptic number.

It is an amenable number.

851021921 is a deficient number, since it is larger than the sum of its proper divisors (50060131).

851021921 is a wasteful number, since it uses less digits than its factorization.

851021921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50060130.

The product of its (nonzero) digits is 1440, while the sum is 29.

The square root of 851021921 is about 29172.2800103112. The cubic root of 851021921 is about 947.6477060567.

The spelling of 851021921 in words is "eight hundred fifty-one million, twenty-one thousand, nine hundred twenty-one".