665857 has 2 divisors, whose sum is σ = 665858. Its totient is φ = 665856.

The previous prime is 665843. The next prime is 665897. The reversal of 665857 is 758566.

It is a Cunningham number, because it is equal to 816²+1.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 665856 + 1 = 816^2 + 1^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665857 is a prime.

It is a super-3 number, since 3×665857³ = 885654153990533379, which contains 333 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (665897) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332928 + 332929.

It is an arithmetic number, because the mean of its divisors is an integer number (332929).

2⁶⁶⁵⁸⁵⁷ is an apocalyptic number.

It is an amenable number.

665857 is a deficient number, since it is larger than the sum of its proper divisors (1).

665857 is an equidigital number, since it uses as much as digits as its factorization.

665857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 50400, while the sum is 37.

The square root of 665857 is about 816.0006127449. Note that the first 3 decimals coincide. The cubic root of 665857 is about 87.3226666977.

It can be divided in two parts, 66585 and 7, that multiplied together give a triangular number (466095 = T₉₆₅).

The spelling of 665857 in words is "six hundred sixty-five thousand, eight hundred fifty-seven".