646781 has 2 divisors, whose sum is σ = 646782. Its totient is φ = 646780.

The previous prime is 646771. The next prime is 646823. The reversal of 646781 is 187646.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 586756 + 60025 = 766^2 + 245^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-646781 is a prime.

It is a super-2 number, since 2×646781² = 836651323922, which contains 22 as substring.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 646781.

It is not a weakly prime, because it can be changed into another prime (646721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323390 + 323391.

It is an arithmetic number, because the mean of its divisors is an integer number (323391).

2⁶⁴⁶⁷⁸¹ is an apocalyptic number.

It is an amenable number.

646781 is a deficient number, since it is larger than the sum of its proper divisors (1).

646781 is an equidigital number, since it uses as much as digits as its factorization.

646781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 32.

The square root of 646781 is about 804.2269580162. The cubic root of 646781 is about 86.4806777428.

The spelling of 646781 in words is "six hundred forty-six thousand, seven hundred eighty-one".