645761 has 8 divisors (see below), whose sum is σ = 685824. Its totient is φ = 606960.

The previous prime is 645751. The next prime is 645763. The reversal of 645761 is 167546.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-645761 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (645763) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 866 + ... + 1428.

It is an arithmetic number, because the mean of its divisors is an integer number (85728).

2⁶⁴⁵⁷⁶¹ is an apocalyptic number.

It is an amenable number.

645761 is a deficient number, since it is larger than the sum of its proper divisors (40063).

645761 is a wasteful number, since it uses less digits than its factorization.

645761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 631.

The product of its digits is 5040, while the sum is 29.

The square root of 645761 is about 803.5925584524. The cubic root of 645761 is about 86.4351926392.

The spelling of 645761 in words is "six hundred forty-five thousand, seven hundred sixty-one".