645520 has 20 divisors (see below), whose sum is σ = 1501020. Its totient is φ = 258176.

The previous prime is 645503. The next prime is 645521. The reversal of 645520 is 25546.

It can be written as a sum of positive squares in 2 ways, for example, as 73984 + 571536 = 272^2 + 756^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a junction number, because it is equal to n+sod(n) for n = 645491 and 645500.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645521) by changing a digit.

645520 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3955 + ... + 4114.

It is an arithmetic number, because the mean of its divisors is an integer number (75051).

2⁶⁴⁵⁵²⁰ is an apocalyptic number.

It is an amenable number.

645520 is an abundant number, since it is smaller than the sum of its proper divisors (855500).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

645520 is a wasteful number, since it uses less digits than its factorization.

645520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8082 (or 8076 counting only the distinct ones).

The product of its (nonzero) digits is 1200, while the sum is 22.

The square root of 645520 is about 803.4425928466. The cubic root of 645520 is about 86.4244386743.

The spelling of 645520 in words is "six hundred forty-five thousand, five hundred twenty".