865721 has 2 divisors, whose sum is σ = 865722. Its totient is φ = 865720.

The previous prime is 865717. The next prime is 865729. The reversal of 865721 is 127568.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 846400 + 19321 = 920^2 + 139^2 .

It is a cyclic number.

It is not a de Polignac number, because 865721 - 2² = 865717 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (865729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 432860 + 432861.

It is an arithmetic number, because the mean of its divisors is an integer number (432861).

2⁸⁶⁵⁷²¹ is an apocalyptic number.

It is an amenable number.

865721 is a deficient number, since it is larger than the sum of its proper divisors (1).

865721 is an equidigital number, since it uses as much as digits as its factorization.

865721 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 865721 is about 930.4412931507. The cubic root of 865721 is about 95.3072600004.

The spelling of 865721 in words is "eight hundred sixty-five thousand, seven hundred twenty-one".