645923440 has 40 divisors (see below), whose sum is σ = 1550222208. Its totient is φ = 250033920.

The previous prime is 645923431. The next prime is 645923441. The reversal of 645923440 is 44329546.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (40).

It is a Smith number, since the sum of its digits (37) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 645923440.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (645923441) 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, 127747 + ... + 132706.

Almost surely, 2^645923440 is an apocalyptic number.

It is an amenable number.

645923440 is an abundant number, since it is smaller than the sum of its proper divisors (904298768).

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

645923440 is a wasteful number, since it uses less digits than its factorization.

645923440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 260497 (or 260491 counting only the distinct ones).

The product of its (nonzero) digits is 103680, while the sum is 37.

The square root of 645923440 is about 25415.0239031955. The cubic root of 645923440 is about 864.4243956985.

The spelling of 645923440 in words is "six hundred forty-five million, nine hundred twenty-three thousand, four hundred forty".