645880 has 32 divisors (see below), whose sum is σ = 1481040. Its totient is φ = 253440.

The previous prime is 645877. The next prime is 645889. The reversal of 645880 is 88546.

645880 = T₁₀₄ + T₁₀₅ + ... + T₁₇₀.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645889) 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, 2560 + ... + 2800.

2⁶⁴⁵⁸⁸⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 645880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (740520).

645880 is an abundant number, since it is smaller than the sum of its proper divisors (835160).

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

645880 is a wasteful number, since it uses less digits than its factorization.

645880 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 319 (or 315 counting only the distinct ones).

The product of its (nonzero) digits is 7680, while the sum is 31.

The square root of 645880 is about 803.6665975391. Note that the first 3 decimals coincide. The cubic root of 645880 is about 86.4405017015.

The spelling of 645880 in words is "six hundred forty-five thousand, eight hundred eighty".