645691 has 2 divisors, whose sum is σ = 645692. Its totient is φ = 645690.

The previous prime is 645683. The next prime is 645703. The reversal of 645691 is 196546.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 645691 - 2³ = 645683 is a prime.

It is an Ulam number.

645691 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (645611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322845 + 322846.

It is an arithmetic number, because the mean of its divisors is an integer number (322846).

2⁶⁴⁵⁶⁹¹ is an apocalyptic number.

645691 is a deficient number, since it is larger than the sum of its proper divisors (1).

645691 is an equidigital number, since it uses as much as digits as its factorization.

645691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6480, while the sum is 31.

The square root of 645691 is about 803.5490028617. The cubic root of 645691 is about 86.4320693567.

The spelling of 645691 in words is "six hundred forty-five thousand, six hundred ninety-one".