851821 has 2 divisors, whose sum is σ = 851822. Its totient is φ = 851820.

The previous prime is 851813. The next prime is 851831. The reversal of 851821 is 128158.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 662596 + 189225 = 814^2 + 435^2 .

It is a cyclic number.

It is not a de Polignac number, because 851821 - 2³ = 851813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (851801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 425910 + 425911.

It is an arithmetic number, because the mean of its divisors is an integer number (425911).

2⁸⁵¹⁸²¹ is an apocalyptic number.

It is an amenable number.

851821 is a deficient number, since it is larger than the sum of its proper divisors (1).

851821 is an equidigital number, since it uses as much as digits as its factorization.

851821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 640, while the sum is 25.

The square root of 851821 is about 922.9414932703. The cubic root of 851821 is about 94.7944215652.

Adding to 851821 its reverse (128158), we get a palindrome (979979).

The spelling of 851821 in words is "eight hundred fifty-one thousand, eight hundred twenty-one".