856721 has 2 divisors, whose sum is σ = 856722. Its totient is φ = 856720.

The previous prime is 856717. The next prime is 856733. The reversal of 856721 is 127658.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 801025 + 55696 = 895^2 + 236^2 .

It is a cyclic number.

It is not a de Polignac number, because 856721 - 2² = 856717 is a prime.

It is a Chen prime.

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (856711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 428360 + 428361.

It is an arithmetic number, because the mean of its divisors is an integer number (428361).

2⁸⁵⁶⁷²¹ is an apocalyptic number.

It is an amenable number.

856721 is a deficient number, since it is larger than the sum of its proper divisors (1).

856721 is an equidigital number, since it uses as much as digits as its factorization.

856721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 29.

The square root of 856721 is about 925.5922428370. The cubic root of 856721 is about 94.9758387310.

The spelling of 856721 in words is "eight hundred fifty-six thousand, seven hundred twenty-one".